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“It is necessary that I should here speak in the first person, in order to convey graphically the first steps of Major Colby's invention. Every one who knew him in those days must remember how rapidly he moved or ran through the streets, rarely relapsing into a simple walk; and it was thus that I met him rapidly descending Tower Hill, when he took my arm, and, with the usual. Come, my boy, I have something to talk to you about,' carried me with him to the Map Office in the Tower, which was not only the office for the business of the Survey, including the engraving of the maps, but also contained the private apartments allotted to Major Colby, as director of the work. When once there I was detained for the evening, and after dinner Major Colby fully explained to me the idea he had formed of a compensation measuring rod. [Here follows an elaborate account of the invention, not as a germ or conception, but as a thing fully and completely devised. The starting-point of the explanation is the gridiron pendulum, the principle of which is explained ; and then follows Colby's plan :- In the mode proposed by Major Colby, two bars of different metals were to be fastened together in the centre,' &c.] Having listened attentively to Major Colby's explanation of the principle of his proposed compensation measuring rods, I felt satisfied that it would succeed in practice; but such was not the opinion of all the members of our little senate, as Lieutenant Drummond was, in the first instance, more disposed to go on with his own inquiries, and expected a better result from them than from the proposed bars of our chief.”*

He proceeds to state that he accompanied Major Colby to Mr Troughton, who at once approved of the plan, and made a small three feet model bar. "The small three feet model bar was rapidly made, and from that moment Drummond became the most able and active assistant of Major Colby in conducting all the preliminary experiments.” Elsewhere he more clearly defines the function which he assigns to Drummond in connection with the bars. “ The laborious experiments,” he says, which

“ Memoir of Colby,” App. II. p. xi.

were made for comparing the standards with the recognised standards of measure, for determining the exact position of the compensated points of the measuring bars, and for examining various descriptions of varnishes in order to fix upon one which would equalise as much as possible, in the two metals, the times required for acquiring any change of temperature (a matter of the utmost importance, as upon that equality depends the perfection of the compensation action, whilst the rapidity of heating and cooling is very

different in different bodies), were carried on by Lieutenant Drummond, assisted principally by Lieutenant Murphy, but occasionally by several of our little band, under the immediate eye of Major Colby, on the basement floor of the Ordnance Map Office. The result was everything that could be desired, and the base of the Irish Survey was measured under the immediate direction of the inventor of the bars in the summer of 1827 with the most perfect success, several portions of the measurement having been witnessed by some of the most eminent scientific men of the country.” He takes no notice of Mr Drummond's experiments in 1826. As to the experiments from which Mr Drummond “expected a better result than from the proposed bars of our chief,” we have the following account, introduced by the statement, that on the Irish Survey being resolved upon, Mr Drummond anxiously set himself to devising a new measuring apparatus.

"The quarters, in Furnival's Inn, of Lieutenant Drummond, became a laboratory and a workshop, and diligently did that highly gifted officer labour to produce a measuring apparatus which should be free from the alleged defects of those hitherto used. His last and favourite scheme was a riband, formed of slips of mica, and which it was supposed would be almost in

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variable in length, from its very low degree of dilatibility. As, however, this riband would have required to be supported, like the measuring rods of Svanberg, by a trussed plank, and to be kept straight by weights, it did not appear to ensure permanency of length, even had it been admitted as true that mica undergoes little perceptible extension by heat. During his trials, Lieutenant Drummond suspended the riband of mica by iron wires, but this system would not have answered in practice, as the expansion of the wires by heat would have affected their rigidity, and rendered different weights necessary for retaining them in one constant state of curvature. Encouraging his officers, as Major Colby always did, to pursue these inquiries, and taking the greatest interest in the results of their efforts, he did not himself remain idle; and though from his apparently careless manner they scarcely looked upon him as a rival, the master soon proved that in the race of invention he was able to beat the most ingenious of his 'boys,' as he familiarly called them."

Several of these statements appear to be incorrect. In Captain Yolland's account of the measurement of the Lough Foyle base, which was published under the direction of Colby, we have the work of each of those engaged in the operations for the measurement assigned to its performer on the evidence of official documents. The invention of the bars is indirectly ascribed to Colby, by a reference in the preface to the reasons by which he was induced to devise a new measuring apparatus. The earliest recorded experiments, however, are those of Drummond in his chambers at Furnival's Inn and the Map Office in 1826, in regard to the rates of heating and cooling of bars of brass, steel, and iron, and the effects, on these rates, of varying the surfaces of the bars. Neither Colby, Murphy, nor any one “ of our little band,” has any place assigned to him in connection with these experiments or those for equalising the rates of changing temperature in the bars, for ascertaining the compensated points, or for putting the bars or microscopes in shape for use. They are assigned purely and simply to Drummond. As to the actual measurement of the base : "It was measured,” says Portlock,“ in the summer of 1827, under the immediate direction of the inventor of the bars with the most perfect success.” He means Colby; but the base was mainly measured under the direction of Drummond. Portlock is incorrect even as to the time when the measurement was made. The measurement was not made “in the summer of 1827.” Late in the autumn of that year measurements and remeasurements amounting to 13,250 feet were made ; but the measurement was mainly made in 1828, in the summer and autumn of which year the measurements and remeasurements amounted to 30,533 feet.* And in 1828, when the work was mainly executed, Colonel Colby (who was present, and in charge of the operation, in the season of 1827) is officially noticed only as having been once on the ground during the whole operations, extending from July 7 to November 18.

“It should be stated,” says Captain Yolland,t “ that the charge of conducting the measurement was principally entrusted to Captain Drummond, who superintended the final examination of the bisection of the compensation points on the bars by the compensation microscope.” He was, in short, “ the officer in charge,” whose numerous duties, before examining the bisection of the points, Captain Yolland fully details. Lieutenant Murphy had charge of the alignment. In a note, Captain Yolland says, “I am indebted for the greater portion of the information, both as regards the adjustments of the apparatus, and the detail of the

* Yolland's “ Account," p. 29. † “ Account,” p. 30.

system followed, to Colonel Colby and Captain Henderson, inasmuch as there is little, besides the actual observations, among the notes and memoranda left in the office by Captain Drummond and Lieutenant Murphy, to enable any person who had not witnessed the operation to become sufficiently conversant with the apparatus to describe it, and the mode of proceeding. Both these officers, I believe [the doubt can apply only to Murphy], were fully acquainted with it, and perfectly masters of the subject; and it is much to be regretted that they were called on to undertake other duties before they had left written, if not printed, accounts of the operations between 1826 and 1834.” Portlock also finds matter for regret in connection with the base measurement. It is to be regretted,he says, “that Major Colby could not have devoted his time immediately to the publication of the details of this beautiful operation, and have thus connected his own name alone with a work so eminently his own.”

This unsatisfactory statement seemed to be further discredited by a letter written by Sir John Herschel to Mr Drummond's mother, May 12, 1840, from which, also, it appeared that Herschel had been at one time uncertain as to the authorship of the bars :—“I am unable decidedly to say, and will not therefore incur the hazard of doing injustice to the talented and estimable officer at the head of that operation, by deciding whether the beautiful and simple idea, by which was performed the compensation for temperature in the rods employed in measuring the base in the plains near Londonderry, originated with himself or with Mr Drummond. It proved as successful in practice as it was perfect in theory, and, in its effects, went to abolish altogether one of the most precarious and annoying corrections in that

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