emed by
J. DUDLEY HERRON Purd~eUnlver~8ty West Lafayette. lndiam 47907
Boyle'slHooke'slTowneley and Power's1 Mariotte's Law Robert M. Hawthorne, J r . l'urdue f!niuursir, .North Centml ('amnus Westoille, I N 46391 Chemistrv, like all the sciences. is filled with constants. principles, i n d mathematical laws, many of which have sumeone's name attached to them. The student of chemistry, knowing no better, is apt toassume that theperson named is the person who actually produced the number or formula that's im the pnKe before him, an assumption often far from tht truth. Probably nogreat harm isdone in this way,asthe whsrnnce of the law is more important than its pn~venance. Nonetheless, there are some interesting anecdotes connected with [he iormulation of laws, or the determination u t ' n x stunts, that can he used to enliven classroom presentations. In some cases the background of these stories can lead to a deeper understanding of the principle itself. A case in point is the gas pressure-volume relationship that we know as Boyle's Law, which has a very tangled origin indeed. T o beein with. it was not orieinallv in the " * exnressed . simple mathimatical form in which we know it: P V = a constant: or PIVI = PIVZ. Second. and even more curiouslv. ".for all its simplicity, it was not worked out by Robert Boyle, even though it was his extensive experimentation and masses of d a t a t h a t set others on the path to do so. Robert Boyle (1627-91), often called the "father of chemistry," showed a consuming interest from early years in both science and theology. By the middle 1650's his self-directed apprenticeship in science drew to a close, and the indefatigable experimentation that would mark the rest of his life was heginning to hear fruit. His curiosity was such that few fields of science were completely closed to him. His published works, gathered into six huge volumes some 80 years after his death,' contain writings of his experiments and speculations on air (i.e., gases), atomism, chemistry and alchemy, color, medicine (both theoretical and practical), heat and thermometry, relative humidity. water analvsis. . hvdrostatics. . . ..ohvsioloev..effects of vacuum on living creatures, and a great number of reports of curiosities, such as: a "monstrous head." animals with milk in their veins in place of blood, mineral waters that petrify wood. an earthquake. blood transfusions and infusions in a n i k l s , lkninescent materials such as wood and decaying fishes, sunspots, and air bladders in fishes. It was not surprising that when Boyle heard of Otto von Quericke's air pump in 165: (the pump used to evacuate rhe famous " ~ a ~ d e b u hemispher&," ig feaving them held together by external air pressure so strongly that oxen could not pull them apart), he lost no time in asking Robert Hooke to design and construct an improved model. Using this pump, Boyle gathered an enormous amount of data on the variation of volume of a gas with pressures below one atmosphere. Later, he extended his investigations to pressurea greaier than one atmosphere, using the mercury-filled J-tube, rlused at one end. All of these exoerimental data were first oublished .- hv Boyle in 1660 in the book, "New E n p e r i m e k physico~~
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mechanicall, touchine- the S .~ r i .n eof the Air." As the title suggests, Boyle was interested in his cxperimt.ntal res111t.ias u demonstration of the elasticity, ur "sprinr." . . oi the air, and the implications that this may have for an atomistic explanatim ot' gas heha\,iur. ?'here i s no marl~cmacrmlhw, uxprvrs or implied, in this first edition. I n 1660 and 1661 Richard Towneley and Henry Power carried out a series of similar exneriments (whether insnired by Boyle's work or not, is not clear), and gave in the language of the time the first statement of the pressure-volume relation: "So that here is now four Proportionals, and by any three given, you may strike out the fourth." T h a t is, given the familiar relationship PIV1 = P2V,, specification of any three of the variables fixes the fourth. They further noted the predictive properties of such a relationship, enabling one to "prognosticate the effects, which follow in all Mercurial experiments, and predemonstrate them, by calculation. . ." 2. In 1661 Hooke repeated Towneley and Power's work and verified their mathematical formulation. He apparently mentioned the fact to B ~ y l ewho , ~ had already received an account of Tovineley and Power's experltnents and conclusion frnm WilliamCroone,nmi~mheroftheRovalSocietv. I n rhi.. way the relationship-in words, not in today's mathkmatical form-came to be included in the second (1662) edition of Boyle's "Experiments.. . touching the Spring of the Air2'with due acknowledgment to Towneley, though Power's name is missing. Thus "Boyle's Law," as it is known in the English-speaking world, was first published by Boyle himself, though the mathematical relationship was not originally his. What of the remainingname in the title of this piece, Edme Mariotte? The law is in fact known on the Continent as "Mariotte's Law." but Mariotte's work was nublished a t least fourteen years after Boyle's, and it appears'that he may even have been familiar with the latter's 1662 oublication. So we may continue to honor the law's English originators in one way or another. This still leaves the trt~uhlesomequestion: \lust we now learn tosay "Towneley and J'ow~r'sJ.au,"? I rhink !,or. How on stubbornly using kilocalories, many of us still Angstroms, or dynes because they're convenient and we're used to them, even though textbooksnowadays assure us that we should be using the proper S I units? I t would be just as difficult to get people to switch to a clumsy locution like "Towneley and Power's Law." But we need a more positive justification to go on honoring Robert Boyle by associating his name with thelaw. The reason exists in the priority of his publication, hut even more importantly in the priority of his laboratory work. That is, Boyle
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Boyle, Robert, "The Works," (Editor Birch, Thomas) 6 vol. Hildesheim, Georg Olms, 1965 (reprint of London ed., 1772). %I.Cohen, Bernard, "Newton, Hooke and 'Boyle's Law,' "Nature,
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Neville, Roy G., "The Discovery of Boyle's Law, 1661-1662," d. CHEM. EDUC., 39 356 (1962). Stimson, Dorothy, "Scientists and Amateurs, A History of the Royal Society," New York, Schurnan, 1948, Plate 5, facing p. 49. Volume 56.Number 11, November 1979 / 741
was the first to design the experiments to gather the data-the right experiments to gather the right data to demonstrate the reciorocalitv of volume and oressure. The findine was his. even thobgh thernathematical fbrmula was not. If some oeoole are still unsatisfied. I will aooeal .. to Bovle's place in the history of science. As much as any man hefoie or since, he directed attention to controlled exoerimentationnot random d~servation,and rerlainly no; deduction from principles eststrli.shed a pnrlr;, outside the laboratory -as the proper way to appwilch scientiticdiscovery. He was the first to do so with such authority and consistency. He was also n figure of sufficient religiuusrredihility 11) srt to rest the fears of many honest churchmen that laboratory investigation of the handiwork of Cod might he ii kind of hliisnhemv-a " a~ ~ ~ - - - - a burning issue a t the time, and even occasionally today, hut one which there is no room to discuss here. No other scientist of Boyle's stature appears in this investigation exceot Hooke. who made no claim to the formulation ofthe law, and in any c k e is well honored in the spring-tension ~
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law and its corresponding modulus which are named after him. Towneley and Power appear to have been talented and enthusiastic amateurs. They were not members of the Royal Society," although they were acquainted with memhers. We may give them their legitimate due as the men who saw the mathematical relation of gas pressure and volume, hut reserve the implied admiration of anamed law for the towering figure of the time, Robert Boyle. I thank Professor Herron for passing on a suggestion from Aaron Ihde, University of Wisconsin, for the topic of this article High School Forum is a monthly feature presenting short articles of interest and use to high school teachers in their work. Contributions to High School Forum from high school teachers are especially solicited. Some teachers may feel that they have more questions to ask than answers to give. These are also invited. Send two copies of all contributionsto the column editor.
