John T. stock University of Connecticut Storrs, 06268
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Thomas Charles Robinson and his
Child (1) tersely states that Rohinson of London began to make analytical balances ahout 1823, was the first to manufacture these on a commercial scale, and was also the first to produce a balance having a triangular perforated beam. According to Child (I), Robinson balances were the first of the precision type to he used in America. Apart from brief comments by Dittmar (2) and by MacNevin (S), Robinson and his balances appear to have escaped treatment in reasonably modern literature. Extensive preliminary inquiries directed to balance makers, museums, universities, learned and professional societies, and similar organizations in Europe and the United States were unfmitful except in one case. Mr. J. R. Waite, of Oertling, Ltd., England, makers of precision balances since about 1840, pointed out that a balance described as similar to those of the late T. C. Robinson had been shown at the London 1851 Exhibition. Besides providing the craftsman's initials, this information fixed the latest possible date of his activities. Early 19th century literature shows that a "Mr. Rohinson" was well known to contemporary scientists. His balances were used in the adjustment of copies of the Imperial Standard Troy Pound in 1825 and 1829 (4, 5). Following the destruction of the Standard by fire in 1834, balances by Robinson and by Barrow were featured in the lengthy work of reestablishment. "In its construction it (the Barrow balance) nearly resembles the balances of the late Mr. T. C. Rohinson." (6). Listings of instruments "made and sold by T. C. Robinson, 38 Devonshire Street, Portland Place, I,ondon," were published in 1829 and 1831 (7). The following appears in the later listing under "Balances for Chemical, Philosophical and Assaying purposes": 1 Beam 10'/* inches long will bear in each pan 2000 Grains.. . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 (Guineaq) 2 Beam 8 inches long ditto 1000 Grains. . . . . . . l l 3 Beam 5'/1 inches long ditto 400 Grains. . . . . . 8 The above Balances have steel knife edges acting with agate plane s~lrfaces,wit,h crystal knife edges instead of steel each size 1 Guinea extra. Larger sizes are also made to order their arrangement embraces several important improvements by Captain Kaler, Dr. Wollaston and the Maker, all the sines are furnished with platinum weights to 100 Grains, and lrpwards of brass. They will indicate ,001 of s. Grain with 1000 Grain.
This indicates Robinson's association with Icater and other scientists, as well as his ability to turn out, on a regular basis, balances sensitive to one part in a million. The reference to "crystal knife edges" is in line with Dittmar's statement that Rohinson was the first to make both knives and bearings of agate (2). The introduction of agate plates as bearings ("planes") in a balance occurred before Robinson's time, apparently at the suggestion of Cavendish (8). It is interesting that 254
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the beam-length of Robinson's smallest instrument is about that of a "modern" short-beam two-pan aualytical balance. Apparently, Robinson made only one contribution to scientific literature (9). This account of a mountain barometer, "communicated by Captain Henry Kater, F.R.S.," carries the author's full name, Thomas Charles Robinson. The account of the replacement of the British Standards of mass is by W. H. Miller (5). He was Professor of Mineralogy in the University of Cambridge and is much better-known to present-day scientists as the originator of the "Miller indices" (10). Closer inquiries in Cambridge showed that the Department of Mineralogy still has a damaged and incomplete lollr in. Robinson balance. I.'ortunately, Robinson was in the habit of engraving his name and address upon his instruments. Two complete 51/z-in.balances are in the University's Whipple Science Museum. Apart from other points of interest, these instruments illustrate Robinson's improvements on his basic design. The earlier balance, shown in Figure 1, was used by W. H. Wollaston, discoverer of palladium and rhodium, who died in 1828.
Figure 1.
The "Wolloston" balance.
According to ICater (11), the pivoted-lever pan arresting system fitted to the baseboard was devised by Wollaston. The agate center plane is in two pieces, an arrangement common both before and after Robinson's time. Advantageous in that the beam can be lifted off at will, the split center plane design requires the careful lining-up of the two halves. Each end plane of this balance is formed by polishing the underside of the steel plate that carries the J-wire to which the hook carrying the pan cords is attached. The center is cut away (Fig. 2a), so that contact with an end knife is not full-length.
(a) Figure 2. balance.
the maximum density of water. Hope succeeded Black in 1795 and occupied the Chair for about 50 years. When tested in 1967, without making any adjustments, the Edinburgh balance exhibited a no-load sensitivity of 1.4 scale divisions per mg. Since one of the left pan cords broke on attempting to add weights, no further measurements were made. The balance, which has steel knives that make full-length contact with agate planes, is generally similar to the incomplete 10'/2-in. and later 5'lrin. instruments a t Cambridge. One feature of the Edinburgh balance that is not present in any of the Cambridge balances is a rider-shifting mechanism that can be operated from outside the case. The guide
( b)
End-plane assembly of lo1 "Wollaston" balance i b l "Miller"
The later balance (Fig. 3) was used by W. H. Miller. Its one-piece agate center plane is &xed to a brass plate that passes through an aperture in the beam and is secured to the top of the column by two large knurled thumbscrews (Fig. 4). Removal of these permits the plate to he withdrawn, so that the beam can be taken
.. Figure 5.
Figure 3.
The "Miller" balance.
off. Each one-piece agate end plane makes full-length contact with its knife and is affixed to the underside of a small brass plate that carries the J-wire (Fig. 2b). The general design of the incomplete 10'/2-in. balance is similar to that of the later 51/2-in. balance; both of the end planes and their mountings are missing, as is the Wollaston arrestment. I n his account of the Chair of Chemistry in the University of Edinburgh, h4acIienzie (19) refers to a balance that is supposed to have belonged to Joseph Black. However, AIacKenzie adds "hut recent investigations by Professor Meldmm cast some doubt upon the v e racity of the description." In fact, a balance used by Black is in the Royal Scottish Museum, Edinburgh. Inspection showed that the University of Edinburgh's balance is a near-perfect "lO'/rin. Robinson" that could not have been associated with Black, who died ' ' when the balance maker was still a child. A much more likelv owner or user was T. =,I I ' I C. Hope, the discoverer of ustrontia,~ and the investi- Figure 4. Beam and orrestment details of the "Miller" balance gator of the temperature of (end-plone assembly removedl.
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The "University
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Edinburgh' bolonce.
bar of this mechanism can be seen in Figure 5 above the right-hand side of the beam. If this mechanism was fitted to the balance case by Robinson, it was indeed an innovation. The rider position numbering on the beam appears amateurish when compared with the engraving on the base of the column. It is possible that provision for the use of a rider was made after Robinson's time. The shortness of the pointer and the silk-cord pan supports are the most obvious features that distinguish a Robinson balance from a 20th century instrument. Both features may have arisen from demands made to Robinson for instruments that could he easily transported. Apart from containing weights, the drawer beneath the balance has recesses for the beam, pans, etc. The length of the pointer is thus limited by the hack-to-front dimension of the drawer. Silk cords are light, easily packed away, and can be readily replaced. As is obvious, they lack the permanence of the other parts. In most other respects, Robinson's design is remarkably "modern." Except for an early hydrostatic halauce with adjustable swan-neck end hearings ( I I ) , all of his balances incorporate knifeand-plane bearings a t the ends, as well as at the center of the beam. He did not invent this arrangement, which is a feature of the remarkable balance made by Harrison (presumably John Harrison, the celebrated horologist, who died in 1776) to the instructions of Cavendish. Ramsden, Fidler, Troughton, and other makers of fine balances in the late 18th and early 19th centuries normally employed a knife-and-plane center hearing, hut made the end bearings of the self-locating knife and-ring type. A very simple arrestment that operates Volume 45, Number 4, April 1968
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only on the components of the center bearing can then be used. Although the use of knives and planes throughout is a superior arrangement, a more refined arrestment mechanism is required. This must operate on the three bearings in the correct order and must accurately locate each knife on its plane when the arrestment is released. Robinson's arrestment mechanism is released by depression of a spring-loaded steel lever that projects from the bottom of the column. Movement of the depressed lever to the right locks the mechanism in the "free" position. The design is much more compact and much less complicated than that used in the Cavendish balance. Robinson obviously paid great attention to the final 1adjustment of his balances. "\\ Each end knife A (Fig. 6) is secured by a single set screw B that enters from the underside of the beam end. An end knife can be brought parallel to the center knife by adjustment of "pressing screws" CC ( I S ) . An oblique slit D near the beam can be forced slightly Figure 6. Robinson's end-knife system (01 front view open by rotation of "push- Iodius'ment b l top view (not to scolel. ins screw" E. This allows h tYe half-beam lengths to be equalized and the three knives to be brought into the same plane. Although ingenious and effective, this method of half-beam adjustment strains the metal and can be disastrous in the hands of an over-enthusiastic mechanic. Screws C and E have transversely drilled heads for the insertion of a miniature tommy bar. The "modern" form of analytical balance is usually considered to have originated in Paul Buoge's description of the theory and construction of the short-beam type (14). Although Robinson may have been no theoretician, his 51/2-in.beam balances are precision instruments, and predate those of the German engineer by about 40 years. Letters to the British scientific (15) and lay (16) press (and even limited advertising!) have produced no further examples of Robinson balances. It is particularly unfortunate that no example of the 8-in. beam balance, or of any balance having L'crystal" or agate knives, has yet come to light. Thomas Charles Robinson was born on September 3, 1792 and was baptized in St. Marylebone Parish Church. His father was Henry Robinson, a haberdasher, hosier, and linen draper at 37 Devonshire Street, Marylebone, until his death in 1809. The widow, Mary, with her children Henry (Jr. b. 1788), Mary (Jr., b. 1789), Thomas Charles, and Charles Robert (b. ca 1803) moved into the adjoining No. 38, where she continued the haberdashery business. The family was gifted; Charles Robert (who died when only 31) and Henry (Jr.) were both pictorial artists. Paintings by Henry (Jr.) were hung in the Royal Academy Exhibitions of several years from 1818 onwards. Possibly Thomas Charles Robinson became an instrument maker after association with clockmaking. His cousin, Henry Blundell, was certainly a clockmaker. Only for the period 1830through 1834 is Robinson listed
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in the London Post Office Directory as a mathematical instrument maker a t 38 Devonshire Street. His ornission before and after this date may have arisen from the location of his premises and the sharing of these with hi mother's business. In those days, 38 Devonshire St. was about 100 yards west of the present-day building of this number and was located on the corner of a n a m w passage called Clark's Mews (now Dunstable Mews). Mary Robinson's business had the greater need for a window display giving on to Devonshire St. Instrument making may have occupied the rear of the premises, probably with access through a side door in the Mews. Directory compilers on their rounds may not often have troubled to look for trade signboards down minor passages. Plans were made to inspect the original but extensively-altered building (17) during the summer of 1967. Wrecking had occurred; a bulldozer was working in the remains. Robinson died of chronic bronchitis on July 25, 1841. His mother was the principal beneficiary under his will, which empowered his executors to fulfill outstanding orders and directed them to sell stock-in-trade and tools. "I will and bequeath to my Apprentice John Dover in testimony of my approbation of his zeal and integrity the sum of five pounds to be paid to him when he attains the age of twenty one years." The Robinson-pattern balance in the 1851 Exhibition was actually made by this John Dover (18, 19). The Devonshire St. address appears on the death certificate, but Robinson was buried with his younger brother in the churchyard of the ancient St. Mary-at-Finchles, some ten &es northward. On the headstone (Fig. 7) can still be read: "Endowed with the highest intellect and devoted to science he attained to eminence in his profession and was highly esteemed." So rests a major fimre in the develbpmeLt of the precision balance. In addition to the acknowledgments contained in the text, grateful thanks are due to the following for permission Figure 7. Headstone of Charles and facilities to emnine Robert Robinron, ortirt, and Thomar Robinson balances: Drs. Chorler Robinson, mothematicol inmaker. N. F. M. Henry (Department of Mineralogy) and M. Hoskin (Whipple Science Museum), University of Cambridge; Dr. D. M. W. Anderson and Mr.T. D. Sheddan, University of Edinburgh. The expert genealogical servioes of Mr. A. K. Henriksen are recognized. Finalization of the work was assisted by a grant from the University of Connecticut Research Foundation. Literature Cited (1) CHILD, E., "The Tools of the Chemist," Reinhold Publishing Carp., New York, 1940, p..81: (2) DIT~MAR, W., in "Thorpe's Dlctmnsry of Applied ChemJ. F. T., AND WHITELY,M. A.,) istry," (Editors: THORPE, (4th ed.), Longmans, Green & Co., London, 1937, Vol. 1, p. 587. (This is an amended form of Dittmar's writing for the fimt edition of the Dictionary, which appeared in 1890).
(3) MACNEVIN, W. M., "The Analytical Balance: its Care and Use," Handbook Publishers, Inc., Sandusky, Ohio. 1951, p. ix. (4) KATER,H., Phil. Trans., 116,1(1826). (5) SCHUMACHER, H. C., Phil. Trans., 126,457 (1836). (6) MILLER,W. H., Phil. Trans., 146,762 (1856). (7) Astronwnische Nach'ehten, 7, 232 (1829); 8, 48 (1831). (8) THORPE,E. (Edilor) "The Scientific Papers of the Honourable Henry Cavendish, F.R.S.," Cambridge University Press, 1921, Vol. 2, p. 56, footnote. T. C., Proe. Roy. Soe., 3.40 (1832). (9) R~BINSON, (10) FINDLAY,A., "Introduction to Physical Chemistry," (Snd ed.), Longmans, Green & Co., London, 1942, p. 157. (11) KATER,H., Quwt. J. Sci., 12, 40 (1822); 11, 280 (1821). (12) MACKENZIE, J. E., J. CHEM.EDUC.,12,503 (1935). D., "Mechanics," in "The Cab(13) KATER,H., AND LARDNER,
inet Cyclopedia," London, 1830, p. 284. (14) B ~ N G E P.,, Rep. Phys. Technik. Math. Aslron. Inst?., 3,269 (1867). J. T., C h . & Ind., (London) 905 (1966). (15) STOCK, J. T., Marylebone Mercury (London), Sept. 2, 1966. (16) STOCK, (This newspaper covers the area. in which Robinson worked.) (17) HARRISON, K. C., private communication, Feb. 6, 1967. (Mr. Harrison is Librarian of the City of Westminster, London, of whichMsrylebone now forms apart.) (18) "Official Description and Illustrated Catalogue, Great Exhibition of the Works of Indxstry of All Nations," Spicer Bras., London, 1851, Vol. I, p. 449. (19) "Reports of the Juries, Exhibition of the Works of Industry of All Nations, London, 1851,'' Spieer Bros., London 1852, Vol. 11,p. 556.
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