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The A B C of Atoms. B y Bertrand Russell. S O X l 4 cm p p . 11 162. New York: E. P . Dutton and Company, 1923. Price: 82.00. The chapt’ers are entitled: introductory; the periodic law; electrons and nuclei; the hydrogen spectrum; possible states of the hydrogen atom; the theory of quanta; refinements of the hydrogen spect,rum; rings of electrons; Xrays; radio-activity; the structure of nuclei; the new physics and the wave theory of light; the ncw physics and relativity; Bohr’s theory of the hydrogen spectrum. There are a number of interesting passages in the book. “The chemical properties of the atom depend, almost entirely, upon the outer ring; so does the light that it emits, which is studied by the spectroscope. The inner rings of electrons give rise to X-rays when they are disturbed and it is chiefly by means of X-rays that their constitution is studied. The nucleus is the source of radio-activity. In radium and the other radio-active elements, the nucleus is unst,able, and is apt to shoot out lit.tle particles with incredible speed,” p. 6. “One of the most asronishing things about the processes that take place in atoms is that they seem to be liable to sudden discontinuities, sudden jumps from one state of continuous motion to another. This mot,ion of an electron round its nucleus seems to be lik6 that, of a flea, which crawls for a while, and then hops. The crawls proceed accurately according to the old l a m of dynamics, but t’he hops are a new phenomenon, concerning which totally new laws have been discovered empirically, without any possibility (so far as can be seen) of connecting them with the old laws. There is a possibility that the old l a m , which represented motion as a smooth continuous process, may be only statistical averages, and t’hat, when we come down to a sufficiently minute scale, everything really proceeds by jumps, like the cinema, which produces a misleading appearance of continuous motion by means of a succession of separate pictures,” p. 9. “When I say that an electron has a certain amount of negative electricity, I mean merely that it behaves in a certain way. Electricity is not like red paint,, a substance which can be put’on to the electron and taken off again; it is merely a convenient name for certain physical laws,’’ p. 2 j . “It is impossible t.o get a ring to hold more than a certain number of electrons, though it has been suggested by Siels Bohr. in an extremely ingenious speculation, that a ring can hold more electrons when it has ot,her rings outside it than when it is the outer ring. His theory accounts extraordinarily well for t,he peculiarities of the periodic table, and is therefore worth understanding, though it cannot yet be regarded as certainly true,” p. 3 2 . “Sound-waves consist of vibrations of the air, or of what.ever mat,erial medium is transmitting them, and cannot be propagated in a vacuum; whereas light-waves require no material medium. People have invented a medium, the aether, for the express purpose of transmitsting light-waves. But all we really know is that the waves are transmitted; the aether is purely hypothetical, and does not really add anything to our knowledge. We know the mathematical properties of light-waves, and the sensations they produce when they reach the human eye, but we do not, know what it is that undulates. TTe only suppose that something must undulate because we find it difficult to imagine waves otherwise,” p. 41. “All this so far is purely empirical. Rydberg’s constant, and the formula for the lines of the hydrogen spectrum, were discovered merely by observation, and by hunting for some arithmetical formula which would make it possible to collect the different lines under some rule. For a long time the search failed because people employed wave-lengths instead of wave-numbers; the formulae are more complicated in wave-lengths, and therefore more difficult to discover empirically. Balmer,. who discovered the formula for the visible lines in the hydrogen spectrum, expressed it in wave-lengths. But when expressed in this form it did not suggest Ritz’s Principle of Combination, which led to the complete rule. Even after the rule was discovered, no one knex why there was such a rule, or what was the reason for the appearance of Rydberg’s constant,. The explanation of the rule, and t,he connection of Rydberg’s constant with other known physical constants, was effected by Niels Bohr, xhose theory will be explained in the next chapter,” p. 48.
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“It was obvious from the first that, when light is sent out by a body, this is due to something that goes on in the atom, but it used t,o be thought. that, when the light is steady, whatever it, is that causes the emission of light is going on all the time in all the atoms of the substance from which the light comes. The discovery that the lines of the spectrum are the differences between tjerms suggested to Bohr a quite different hypothesis, which proved immensely fruitful. He adopted the view that each of the t,erms corresponds to a stable condition of the atom, and that light is emitted when the at,om passes from one stable state to another, and only then. The various lines of the spectrum are due, in this theory, to the various possible transitions between different st,able stages. Each of the lines is a statistical phenomenon: a cert,ain percentage of the atoms are making the transition that gives rise to this line. Some of the lines in the spectrum are very much brighter than others; these represent very common transitions, while the faint lines represent very rare ones. On a given occasion, some of the rarer possible transitions may not. be occurring a t all; in that case, the lines corresponding to these transitions will be wholly absent on this occasion,” P. 49. “Einstein’s work has immense philosophical and theoretical importance, but the changes which it introduces in actual physics are very small indeed until we come to deal with velocities not much less than that of light. The new dynamics of the atom, on the contrary, not merely alters our theories, but alters our view as to what actually occurs, by leading t,o the conclusion t.hat change is often discontinuous, and that most. of the mot,ions which should be possible are in fact impossible. This leaves us quite unable to account for the fact. that, all the motiocs that are in fact possible are exactly in accordance with the old principles, showing that the old principles, though incomplete, must be true up to a point. Having discovered that the old principles arc not quite true, we are completely in the dark as to why they have as much truth as they evidently have. No doubt the solution of this puzzle will be found in t’ime,but as yet there is not the faintest hint as to how the reconciliation can be effected,” p. j 7 . “A t,heory which explains all the known relevant facts down to the minutest particular may nevertheless be wrong. There may be other theories, which no one has yet thought of, which account equally well for all that is known. We cannot accept a theory with any confidence merely because it explains what is known. If we are to feel any security, we must be able to show that no other theory would account for the facts. Sometimes this is possible, but, very oft.en it is not. PoincarB advanced a proof t’hat the facts of temperature radiation cannot be explained if we assume that radiation is a continuous process, and that any possible explanation must involve sudden jumps such as we have in t,he quantum theory. His argument is difficult, and it is possible that it may not ultimately prove wholly cogent. But, it affords an instance of that further step without which scientific hypothesis must remain hypothetical,” p. 79. “Radio-activity is one of those processes of degeneration (in a certain technical sense) to which no converse process of regeneration is known. We see complex atoms breaking up, and it is natural to suppose that there are (or have been) circunistances under which they are put together out of simpler atoms. But no trace of any such circumstances has been discovered. I n this respect, as in some others, the universe seems like a clock running down, with no mechanism for winding it up again. All the uranium in the world is breaking down, and we know of no source from which new uranium can come. Under these circumstances it seems strange t,hat,there should be any uranium. But if, like some insects, we lived only for a single spring day, Tre should think it st,range that there should be any ice in the world, since we should find it always melting and never being formed. Perhaps the universe has long cycles of alternate winding-up and running-down; if so, we are in the part of the cycle in which the universe (or at least our portion of it) runs down. Everything pleasant is associated with this running down, because it is only this process that liberates energy for the purposes that we regard as useful. It is t’ime, however, to return from these speculations to the mechanism of radio-activity,” p. 1 1 2 . “The fact that the atomic weights are whole numbers, t,ogether wit,h the facts of radioactivity and of Rutherford’sbombardment, lead irresistibly to the conclusion that the weight
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of an atom is due to helium nuclei and hydrogen nuclei which exist, together in its nucleus. The over-crowding in the nucleus of a heavy atom must be something fearful. Radium C, which emits the a-particles that Rutherford used in his experiments, has a nucleus whose radius is about, three million-millionths of a centimet,re (about one million-m.illionth of an inch). Its atomic number is 83 and its atomic weight is 2 1 4 . This means that in this tiny space it must contain j 3 helium nuclei and 2 hydrogen nuceli; it must also (as we shall see in a moment) contain 131 electrons. It, is no wonder that helium nuclei and electrons move fast when radio-activity liberates them from this dum,” p. 127.
“In the physics of the atom, as it has become in modern times, everything is at,omic, and there are sudden jumps from one condit,ion to another. The elect,ron and the hydrogen nucleus are the true “atoms” both of electricity and of mat,ter. According to t,he quantum theory, t,here are also atomic quantities, not of energy as was thought when the theory was first suggested, but of what is called “act.ion.” The word “act,ion,” in physics, has a precise technical meaning; it. may be regarded as the result of energy operating for a certain time. Thus if a given amount of energy operates for two seconds. there is twice as much action as if it operated for one second; if it operates for a minute, there is 60 times as much action, and so on. If twice the amount of energy operates for a Fecond, there is again twice as much action, and so on. If the energy which is operating is variable, and we wish to estimate its action during a given time, we divide t.he t>imeinto a number of little bits, during each of vhich the energy will vary so little that it may be regarded as constant; we then multiply the energy duking each little interval of t,ime by the length of the interval, and add up for all the intervals. As we make the intervals smaller and more numerous, the result, of our addition approaches nearer and nearer to a certain limit; this limit we define as the total action during the total period of time concerned. rlct,ion is a very important conception in physics; from the point of view of theory it is more important than energy, which has been deposed from its eminence by the theory of relativity. Planck’s quantum h is of the nature of action; thus the quantum theory amounts to saying that there are at,orns of action,” p. 134. “It must be confessed that t,he quantum principle in its modern form is far more astonishing and bewildering t,han is its older form. It might have seemed odd that energy should exist in little indivisible parcels, but at any rate it was an idea t,hat could be grasped. But in the modern form of the principle, nothing is said, in the first instance, about what is going on at a given moment, or about atoms of energy existing at all times, but only about the t,otal result of a process t’hat takes time. Every periodic process arranges itself so as to have achieved a certain amount by the time one period is completed. This seems to show that nature has a kind of foresight, and also knows the integral calculus, without which it is impossible to know how fast to go at each instant so as to achieve a certain result in the end. All this sounds incredible. KO doubt the fact is that the principle has assumed a complicated form because it has forced its way through, owing to experiment,alevidence, in a science built upon tot,ally different notions. The revolution in physical notions introduced by Einstein has as pet by no means produced it,s full effect. When it has, it is probable that the quantum principle will take on some simple and easily intelligible form,” p. 139. “The theory of relativit’y has shown that most of traditional dynamics, which was supposed to contain scientific laws, really consisted of conventions as to measurement, and mas strictly analogous t’o the “great law” that there are always three feet to a yard. In particular, this applies to the conservation of energy. This makes it, plausible to suppose t)hat every apparent law of nat,ure which strikes us as reasonable is not really a law of nature, but a concealed convention, plastered on to nat,ure by our love of what we, in our arrogance, choose to consider rational. Eddington hints that, a real law of nature is likely to stand out by the fact that it appears to us irrat,ional, since in that, case it is less likely that we have invented it to satisfy our int,ellectual taste. -4nd from this point of view he inclines to the belief that t’he quantum-principle is the first’ real law of nature that has been discovered in physics,” p. 158. Wilder D.Bancroft
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Regeneration. By Jacques Loeb. 24x16 cm; pp. I43 New Yorlz and London: McGraw-
Hill Book Company, 1024 Price: 82.00. The final revision of this book was finished by Loeb just before his death. The first part deals with mutilation and regeneration, and the chapters are entitled : introduction; general remarks about the material and the experiments; regeneration and mass relation in isolated leaves of Bryophyllum; the inhibiting action of the rapidly growing notches on the other notches of a leaf; the influence of gravity on the formation of roots and shoots in a detached leaf of Bryophyllum; why does separation of a leaf from the plant induce the growth of roots and shoots in a leaf?; the validity of the mass relation for regeneration in a defoliated piece of stem of Bryuphyllum calycinum; the rble of the inhibiting effect of rapidly growing parts in the regeneration of the stem. The second part deals with polarity in regeneration, and the chapters are entitled: the influence of the leaf on the regeneration in the stem; the influence of gravity on the polar character of regeneration in a stem of Bryophyllum ( 2 ) ; the inhibitory action of apical leaves on the formation of shoots in the lower part of the stem; callus formation; inhibitory effects of a second order by an apical leaf; the inhibitory effect of an apical leaf on shoot formation in a stem suspended horizontally; the growth of the axillary shoots; some preliminary experiments on the path of the ascending and descending sap in the stem of Bryophyllum; concluding remarks. “About a generat,ion ago biologists devoted considerable time to a discussion of the vitalistic and mechanistic conception of life processes. The impulse for this discussion was given a t that time by the experiments of Roux and of Driesch upon the development of eggs, parts of which had been destroyed or removed in the first stages of segmentation. I t was generally or frequently observed that the development of the mutilated egg resulted in the formation of a normal organism. Driesch maintained that t’hisphenomenon could not be adequat,ely explained on a purely physico-chemical basis, but that in addition a metaphysical guiding principle inherent in the organism as a whole was to be postulated. The opposite view wrts held by Roux. The controversy was never settled, for the simple reason that on account of the microscopic size of the egg cells the experiments of both authors had to be purely qualitative. An adequate explanation of natural phenomena is possible only on the basis of quantitative experiments and such an explanation consists in the derivation of the results from a rationalistic mathematical formula (a so-called “law”) without the introduction of arbitrary constants,” p. v. “The writer has for a number of years conducted quantitative experiments on the regeneration of a plant, Bryophyllum calycinum, which have made it possible to correlate the process of regeneration with the quant’ityof chemical material. By comparing the dry weight, of the regenerated shoots and roots with the dry weight of the leaves or stems which were used for regeneration, it could be shown t’hat in the presence of light the quantity of regeneration was under equal conditions of illumination, temperature, and in equal time in direct proportion to the mass of the leaves of stems from which regeneratlion started. If we make the legitimate assumption that the material required for the formation of newshoots or roots was under the conditions of our experiments produced by the chlorophyll contained in the leaf or stem, it follows that the quantity of regeneration is determined in this case by the mass of material available in the stem or leaf for synthetic processes. Under the guidance of this mass relation (which may be, in part at least, identical with the law of mass action), it could be shown that mutilation of the plant leads to a collection of sap in places where it would not have collected without the mutilation. This accounts for the fact that mutilation leads to growth in places of the organism where no growth would have occurred without mutilation. The process of regeneration was thus revealed as a purely physicochemical phenomenon, leaving no necessity nor room for the postulation of a guiding principle aside from the purely physico-chemical forces,” p. vi. “It requires several weeks for a leaf or stem to produce new shoots and roots of sufficient quantity to permit exact weighings. If the time allowed for regeneration is too short, so that the roots and shoots are too small, the error made in cutting off the roots and shoots becomes considerable, since it is not possible to cut off these organs at their base with absolute accuracy. On the other hand, when the shoots reach a considerable size, they participate
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to an increasing degree in the assimilation. As long as their assimilating mass is small compared with the assimilating mass of the leaf on which they grow, the error committed in neglecting this influence is small; if necessary it can be corrected by deducting the mass of the shoots from that of the leaf in calculating the influence of the active mass of the leaf on the production of roots or shoots. The writer carried on his experiments for about three or four weeks; in this time the mass of roots and shoots produced under the conditions of temperature and light prevailing in the greenhouse was sufficiently large to make the error committed in cutting off the roots and shoots comparatively small. In order to rule out accidental variations, each experiment was made on a larger number of leaves or stems, rarely fewer than six in one experiment,” p. IO. “ l t is obvioiis that the leaves suspended in air form a much smaller quantity of dry weight of shoots and roots per gram of dry weight of leaf during the same time and under the same conditions than the leaves dipping into water. Hence, if we accelerate the growth of some notches in the leaf, e . g., by dipping them into mater, we thereby inhibit the growth in the other notches. “When leaves are suspended entirely and permanently in air, practically all the notches commence t o form shoots and roots, but not all will continue to grow. Pome notches will grow more rapidly than others and all the material will flow to the more rapidly growing notches. This explains why ultimately only a limited number of notches will continue to grow in air, usually in the more fleshy parts of the leaf. “The fact that the sap available in a leaf flows to those notches where the growth is most rapid can be seen directly in leaves which form a purplish pigment (probably anthocyanin). This occurs only in leaves of Bryophyllum suspended in air, not in leaves which dip into water,” p. 2 2 . “ T e now understand why the leaf of Br:/ophyllum calycznum, when it is detached from the plant, forms shoots and roots in its notches while this regeneration is inhibited when the leaf forms part of a normal plant. The leaf connected with a normal plant can be dipped into water without forming roots or shoots in its notches. All the material which might be available for shoot and root formaticin in the leaf is sent into the stem. During rl recent visit in Bermuda, I have had a chance to examine thousands of plants of Bryophyllzcm calycinum without finding a single case where a leaf connected with a plant had formed roots or shoots. The same has been true in my greenhouse, and only recently have I had an opportunity to observe about six plants, the older leaves of which formed some tiny shoots. The plants in which this occurred were old and in two boxes containing no other plants; so that the suspicion is justified that their roots had suffered some common injury or disease. When a stem contains many leaves, and when the growth of the stem is stopped or when the sap flow has suffered, it is possible that shoots and roots may originate on leaves still connected with the stem. All that is needed for such growth is that the flow of material from the leaf into the stem should be partially or completely prevented,” p. 41. “It is the purpose of this little volume to show that a simple mass relation can be used as a guide through the bewildering maze of the phenomena of regeneration. This mass relation states that equal masses of isolated sister leaves produce, under equal conditions of illumination, temperature, etc., approximately equal masses of shoots and roots in equal time. With this relation it was possible to explain why isolation of a leaf leads to regeneration; namely, because the material available in the leaf for growth flows normally into the stem where it is used for the growth of roots, shoots, and of the stem itself. When a piece of stem inhibits the regeneration in a leaf the stem gains in dry weight to an amount equal t o the diminution in the dry weight of shoots and roots in the leaf due to the stem. I t was shown that this mass relation holds also for the the formation of roots and shoots in an isolated piece of the stem. Equal masses of stems produce under equal conditions of illumination, temperature, etc., approximately equal masses of roots and shoots in equal time. “In both cases a second physiological factor was revealed which must be considered; namely, that the flow of sap in a leaf or stem is secondarily directed towards that part of a k a f or stem where the more rapid growth of shoots or roots occurs. This explains why only
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some but not all of the anlagen for roots or shoots in a leaf or stem will persist in growing out; while the growth of the others will stop. This again would have remained merely a hypothesis had it not been possible to prove it quantitatively on the basis of the mass relation. “A further complication arises in the fact of the polar character of the regeneration of roots and shoots in the stem of Bryophyllum. Two possibilities presented themselves for the explanation of this phenomenon: the polar character of the regeneration in the stem is either due to a difference in the chemical character of the ascending and descending sap or to a. difference in t,he nature of the cells or anlagen which are primarily reached by the ascending and descending sap. I t was possible to decide between the two hypotheses by using the mass relation, inasmuch as it could be shown that the shoots and roots formed in a piece of stem, increase with the mass of the leaf attached to the stem. Since the sap in the leaf forms shoots and roots in the same notch when the anlagen for these two organs exist closely together, the fact that shoots are formed a t one and roots a t the other end of a stem indicates that the ascending and descending sap of a leaf reach primarily different anlagen, and this conclusion was corroborated by two groups of facts; first, by directing with the aid of gravity the ascending sap in a stem to the tissues capable of root formation roots were produced in abundance by the ascending sap; and second, the mass of shoots produced in the basal part of the stem increased with the mass of an apical leaf. These facts seem to eliminate the idea that the polar character of regeneration is due to any chemical differences between the ascending and descending sap although such differences exist. “The fact Iha t certain mysterious eubstances like the “vitamines” or “hormones” may accelerate the rate of growth of an organ and consequently perhaps also the rate of regeneration, is neither in contradiction with the mass relation nor with its application to phenomena or regeneration. The sap sent out by a leaf contains probably all the substances needed for growth, inclusive also of “vitamines” and “hormones.” “It is quite probable that the principle of mass relation can serve as a guide in phenomena of regeneration in other organisms than Bryophullum. In order to apply the principle we must be able to measure with a certain degree of accuracy the quantit’y of the material available for the synthetic processes underlying regeneration. This is possible in plants wherc the leaf is the main organ for the production of this material and where the light is the main source of energy for its production. I t is also possible where we deal with definite quantities of stored mat,erial, as e. g., in a potato, and where therefore the quantity of the mass of material available for regeneration can be varied a t will. Unfortunately it is not easy to control the mass of available material for regeneration in animals. The material from which new organs are regenerated in animals must be furnished either by the food taken up or by the hydrolysis of material in the cells of the animal. 411 attempts to arrive a t a rationalistic theory of regeneration in animals will have to rely on the use of organisms where the mass of material available for regeneration can be controlled as easily as in Bryophyllum,” p. 141. Wilder D. Bal-croft The States of Aggregation. By Gustav Tammann. Translated b y R. F . Mehl. 2 2 x 1 5 cm; p p . xi 297. New York: D. Van Nostrand Company, 1925. Price: 85.00. This is a welcome translation from the second German edition of Tammann’s well-known book. The chapters are entitled: the states of aggregation; the equilibria of the states of aggregation; equilibria between vapor and liquid; the equilibrium curves; the melting curve; polymorphism; the phase diagram; the deformation of crystals and its consequences; the transition of an unstable into a stable state of aggregation; liquid crystals.
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Boric anhydride appears to be a substance which does not crystallize a t any temperature under atmospheric pressure, p. 38. With increasing pressure the melting-points of the tertiary alcohols are said to pass through a maximum, p. 96. From the pressure-temperature curves for the different modifications of ice, the author considers it possible that they may be isomers with a molecular weight of 54, p. 148.
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“It is a fact worthy of notice that in some cases an expected transition will not occur, or will occur very irregularly, under ordinary conditions, but that in the presence of some medium the transition will take place promptly and completely. Such a case in the transition of ordinary tin into grey tin (transition point 20’) which ordinarily occurs very irregularly and with a great amount of supercooling. In contact with a solution of SnCli the transition is regular, though requiring a good length of time for completion. Evidently the number ,of transition centers on the surface of the tin is greatly increased by the medium. “The influence of dissolved admixture upon the transition point is also of interest. The crystal Hg,Tl*, m. p. 14.4’, in the pure stat’e shows no transition point. An addition of 0.0038 percent Pb causes the appearance of a very significant transition point upon the cooling curve a t 12-13’, accompanied by a discontinuous change in volume,” p. 124. “The blue earth in which diamonds are found imbedded may have worked up as olivine from a depth of 20-30 km., corresponding to a pressure of 6000-9000 kg./cm.z and a temperature of 13ooo-1joo’. Rapid cooling to 1000’ could have produced the diamond as such. But there still remains a degree of uncertainty about the matter, for the beginning of the formation of graphite in diamond a t IOOO’C.is distinct after a period of twenty-four hours, whereas the half-liquid magma must have maintained a temperature above 1000’ for a period considerably greater than twenty-four hours after the pressure had fallen to small values, and yet no paramorphs of graphite or of diamond have been found in the blue earth. Laboratory experience has shown that the important factor in the production of a new crystalline form is the temperature to which the original crystalline form is allowed to fall. A t a definite temperature, in the course of the cooling, the number of crystallization centers increases very greatly, and in view of this fact it may be seen that a diamond crystal that had been once cooled would be much less stable a t a temperature of 1300~-15oo’than one that had never been permitted to cool. “With respect to the artificial preparation of diamond it may be said that the transformation velocity of diamond decreases rapidly with the temperature upon a steep transformation curve, as, for example, upon the transformation curve of Ice I into Ice 11. Experimental difficulties are multiplied by the fact that, cylinders made of material with the greatest strength a t high temperatures are likely to expand so greatly a t a temperature of 1000’ with pressure as low as 3000 kg. that the desired pressure rise of 6000-10,000 kg. becomes impracticable. Whether or not the transformation velocity of graphite into diamond at 1000’ is noticeable cannot be said. At best such an artificial production of diamond would produce no large crystals but only a fine-grained crystalline conglomerate which could find use as an abrasive,” p. 185. “If a slowly increasing force be allowed to work upon a cube cut from a plastic crystalline conglomerate, such as copper, there will be seen upon microscopic investigation of the polished plane of the crystal parallel to the direction of pressure, fine, dark, parallel lines, in the individual crystallites. These gliding-lines are the traces of gliding-planes upon which the portions of each crystallite are displaced with respect to each other, and are so oriented to the direction of pressure that they exert a minimum of resistance to permanent deformation. The pressure a t which the gliding-lines appear corresponds to the elastic limit, which may be exactly determined in this way. The elastic limit obtained for the operation of a pressure agrees with that found upon the application of tension. If the pressure be raised further, these gliding-lines appear in other crystallites, and with increasing pressure the angle of the gliding-line with the direction of pressure becomes sharper, and fina.lly new sets of gliding-lines appear in the crystallites, intersecting the original set of parallel lines. “The explanation of the fact that the gliding-planes do not form in all crystallites a t the same pressure (with copper the first gliding-lines appear at 203 kg./cm.a, and the last at, 2000 kg./cm..) lies in the fact that the force a t which gliding takes place in a crystal depends in great degree upon the orientation of the crystallites with respect to the direction of the force. “Accordingly, all crystallites are finally divided by several systems of gliding-planes, and in this condition each crystallite can endure further deformations of a much greater magnitude. The piece, now divided into numberless small elements-as high as 1000 to
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I ,OOO,OOO elements have been counted in a single crystallite-has obtained the ability to flow. K i t h copper, the pressure a t whirh flow begins, lies a t about 2780 kg./cm.., and therefore exceeds the elastic limit thirtyfold.” p. 200. “Cold work upon a piece of metal causes the formation of laminated fragments to take place within the metal. With sufficient temperature increase very small, new crystallites appear a t the boundaries of the laminated fragments, and these new crystallites increase in size until finally the whole piece consists of well-developed grains. Corresponding to the structural changes there also occur changes in the physical and chemical properties of the metal. In metallography this process is termed recrystallization. d somewhat similar process takes place in the union of the particles of amorphous bodies, and in the combination of liquid droplets to larger drops, but between the agglomeration or coalescence of isotropic particles and the union of anisotropic particles, a difference exists ,with respect both to the beginning of the process and to the structure of the end-product. At the beginning of the combination of anisotropic fragments there are formed, as has been shown with iron and copper, minute new grains at the boundaries of the fragments, whereas in the combination of amorphous fragments the process consists merely in a combination of two or more grains into a larger grain. The end-product of recrystallization is a crystalline conglomerate, the crystallites of which are separated from each other either by voids or by layers of varying thickness made up of non-isomorphous admixtures, whereas the combination of isotropic surfaces of the same composition leads t o a physically homogeneous mass. “The process of recrystallization plays a dominant r81e in many geological processes, such as the formation of glaciers, the production of marble from limestone, and the formation of crystalline schists. The process is of importance in the technology, not only of metalography, but also of ceramics. Unfortunately the workers in fields differing so much as these have little opportunity for the exchange of observations, and the valuable facts known t o the one group have often remained unknown to the other,” p. 205. “The weight of many layers of snow deposited upon glaciers causes the snow crystals to form a grain-like glacier ice. In time this coarsely crystalline aggregate becomes clear, and in the coarse of years the size and character of the grains alter considerably. Accordingly, the undermost ice a t the end of the glacier is made up of grains quite different from the grains formed first. Besides the grains of the sizes of a pin-head and a hazel-nut present in old glacier ice, there are frequently found gigantic grains I O em. in diameter. The grainlike structure of artificial ice of the clear glacial ice formed first upon the compression of the snow crystals is quite easily seen, especially when the grains in the ice are displaced relatively to one another by compression. I n the new glacier ice the grains are generally irregularly oriented with respect to one another. In time, however, in addition to the growth of the grains, a re-orientation takes place so that in large masses of ice all of the grains have parallel optical axes. Investigation of this a t different points upon Alpine glaciers has given different results with respect to the spreading of the sphere of similar grain orientation. E. v. Drygalski observed in old inland ice and in the deeper layers of icebergs of the antarctic the presence of grains varying in size from that of a pinhead to that of a hazel nut, which were optically similarly oriented,” p. 2 1 7 . Tammann notes, p. 2 3 j, that a beautiful blue glass ran be obtained by a suitable heating of difficulty fusible Jena glass. Since he does not add a black background, he has no real conception how beautiful these blues may be. “If a liquid consist of tTvo or more kinds of molecules, polymers, or isomers, and if the equilibrium b e k e e n these molecules be dependent upon the temperature, the crystallization velocity can then be independent of the te nperature only in the case where the equilibrium characteristic to the melting-point produres itself very rapidly, when the liquid is warmed to the temperature of the melting point,” p. 270. On p. 290 is the statement that the bright colors observed when cholesterol esters solidify slowly depend on the size of the spherulites suspended in the melt. This is inaccurate. The colors are a Christiansen effect and vary with the temperature.
Wilder D. Bancroft
