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, "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.

+

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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. 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

It

most delicate and difficult geodetical operation. To whichever be due the credit of originating this invention, the details of the contrivance and the execution of the project devolved on the latter, who, in accordance with what seems to have been a constant principle in his conduct, to leave nothing undone to ensure success, not content with entrusting, as many would have done, the adjustment of the compensation to an instrumentmaker, himself executed, in the midst of furnaces, ovens, and freezing mixtures, all the trials, manipulations, and measurements necessary to ensure success.

"An anecdote may be mentioned here, which sets in a strong light this leading principle of hearty devotion to his object and its duties, to the exclusion not only of personal ease, but to the utter abnegation of all that egotistical feeling which induces so many to turn aside from suggestions of another with indifference, if not with aversion. While engaged in these operations the conversation between himself and a scientific friend happened to turn on the discovery of Mitscheclich, who had shown that in certain crystallised substances heat occasions expansion in some directions, and contraction in others, necessarily implying invariability in some intermediate directions. It was suggested, as a bare possibility, that such a condition might be satisfied by cutting mica in some certain direction to be ascertained by trial, in which case an inexpansive or naturally compensated measure would be obtained. Nevertheless, some time afterwards, the writer of these lines, happening to visit him in his apartments at the Tower, found him surrounded by strips of mica, and busied in working out the suggestion. The result, however, proved abortive in everything but the illustration of character it afforded."

It seemed at variance with the character here ascribed to Drummond by one who knew him well, that he alone "of our little band" should have been indisposed to entertain the principle of compensation from giving the preference to an idea of his own. It appeared also that Portlock misunderstood the object of the mica experiments, which was to procure a naturally self-compensated measure; and further, that these experiments, instead of having preceded those for constructing the compensation bars, were entered upon and abandoned in 1827, when the bars were in the course of being constructed. The basis of Portlock's case for Colby seemed to be thus seriously impugned. In this state of the facts it was felt that the merit of the invention should not be surrendered to Colby, except on evidence of a much more precise and satisfactory character being adduced.

Such evidence was after a time furnished by General Larcom. It appears that the bills of Troughton and Simms have been preserved in the Ordnance Survey Office, and show that the mica experiments belong to the spring and summer of 1826, and are of earlier date than any of the recorded experiments on the expansions and contractions of brass and iron bars and cylinders. It also appears that Mr Browning, who assisted Mr Drummond in the year 1826, is distinct in his recollection that the mica experiments were carried on in Furnival's Inn.* Larcom and Dawson are also clear in their recollections to the same effect, as will be

*The following entries occur in the bills of Troughton and Simms :

"23 Mar. 1826. Apparatus for straining wire in mica experiments, £2.

"1 June 1826. Brass mountings, adjustments, &c., applied to apparatus employed in mica experiments, £1, 10s."

seen from the subjoined extracts from a memorandum written by General Larcom :

My conviction with regard to the relative shares of Colby and Drummond in the design and execution of those instruments is that to Colby belongs the design, to Drummond the execution. Colby having himself used the previously existing English apparatus, and being familiar with the various instruments which had been used in the measurement of bases elsewhere, considered a new apparatus necessary. He resolved to adopt the compensation principle, and devised the form. He first satisfied himself the principle was sound, and tested the mechanical difficulties, which, he found, were all surmountable. He then devolved on Drummond the duty of superintending the construction, which Drummond, with the invaluable assistance of Troughton, successfully accomplished.

"The grounds on which I rest this statement of the relative shares of Colby and Drummond in the base apparatus are, personal knowledge and daily intercourse with all the parties concerned, having been myself one of the officers at the Tower at the time, and taking part in the early operations in the cold cellar and heated chamber, having been more than once at Troughton's with Colby, and often with Drummond in the evenings at Furnival's, where I also lived. No one at that time thought of Drummond as the inventor of the bars. He never claimed to be the inventor, and, I believe, would have been the first to repudiate the idea.

"But that does not derogate from his merit. He made the bars, was the deviser and planner of the numerous and beautiful contrivances and experiments by which they were brought to perfection, and with his own hand executed most of the experiments. I find among my letters from Colonel Dawson, in October 1840, when I was writing my own brief memoir of Drummond, the following paragraph:- Drummond's indefatigable exertions in the construction of the bars, and in the measurement of the base in Ireland, you are yourself aware of. The principle on which the compensation depends was suggested by Colonel Colby, and the means by which it should be supplied; but great credit is still due to