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him of pursuing the higher studies in which he delighted, at the college and in classes, and among the scientific society of his native city. He found the duties, however, so trivial, and the prospects of the service so disheartening, that for some time he meditated leaving the army for the bar, and had actually entered his name at Lincoln's Inn with this view.” That he should have been disheartened, is not surprising. In his letters in the spring of 1818, he complained of his prospects, and longed for, what he saw no chance of, active employment. If that feeling could spring up at Chatham, it must have grown in Edinburgh. And in the interval he had suffered various annoyances from those in authority, too slight to be recorded here, but which would tend to engender disgust at the service. The indifference of the head office to the pontoon inventions would not diminish the feeling.
It is a curious speculation what his career would have been had he embraced the profession of the law. When, at a later date, he gave up science for politics, it was the complaint of many that he was deserting his natural calling
He was in every respect," Sir John Herschel has said to me, “a most excellent person. There was but one ground of complaint I ever had against him—that he deserted science. That was his natural field, and he had every qualification for the highest eminence in it.” Sir Thomas Larcom tells me
* We have a glimpse of one class of his occupations during this stay in Edinburgh. The Rev. A. Craig, of Buccleuch Place, encloses, at Mrs Drummond's request, his account for services in reading Greek with Lieutenant Drummond for the three months ending March 25, 1820. “I cannot speak in too high terms,” he says, " of Lieutenant Drummond's talents and diligence while he read with me, and I was very sorry that his studies were rather prematurely interrupted by his being so suddenly called off.”
that he has known Dr Romney Robinson, the astronomer of the Armagh Observatory, to break into censure of Drummond for “deserting science,” as he called it ; ending by the reflection, that if his poor friend had not committed that one fault, his life might have been spared to the country. And yet, when Drummond became political, he had all the success that could be commanded by a specialty for politics. The fact is, his talents were so great, and his cultivation so general; his sense so sound and manly, and his sympathies so warm and generous; he combined high intellectual with the best personal qualities, and, being an indefatigable worker, must have succeeded in anything to which he deliberately chose to apply himself. Probably, had he in 1819 “ deserted” the military service for the law, he would only the sooner have been brought into political life. I cannot doubt that he would have attained forensic eminence.
His own views as to the spirit in which a man should choose and enter the profession of the law, happen to be preserved. A friend being desirous to join the Scotch bar, Drummond, in a letter from Plymouth, urged several reasons against his doing so--the chief being that he had not the natural qualifications to attain eminence in the profession.
“ Were his nature and energy of such a kind as to justify any reasonable expectations of his distinguishing himself at the bar, I should say no more.
No situation could be more honourable or respectable. But I am convinced, and 'tis useless to conceal it from him, if he has not already found it out, that he must alter materially, or he is not suited for the bar. To succeed in so arduous a profession, he must enter it with all the ardour of enthusiasm and determination to succeed; he must look upon his want of friends, and other such obstacles, as so many triumphs to be obtained and so many trophies to be won.” This is as forcible as it is frank, and (as the event proved) it was true. The aspirant proposed to give up a profession in which he was engaged. Apropos of this, Drummond proceeds :-“ There are many instances of men embracing one profession and rising to eminence in another ; but I fear there is an essential difference between such characters and his, not so much in point of abilities, as in ambition, eagerness, and exertion.” It is clear he had been carefully considering the conditions of success in the legal profession, which many of “ the briefless” only begin seriously to do after years of disappointment. Had he thrown himself into it, no doubt he would have laboured in it with untiring zeal. Such, however, was not to be his career.
In the autumn of 1819 he became acquainted with Colonel Colby, when that officer was in Edinburgh on his return after the summer operations of the Ordnance Survey in the Scottish Highlands. When Colby, in 1820, was appointed successor to Mudge as superintendent of the survey, Drummond received from him and gladly accepted an offer to take part in the work. It was an opportunity of combining scientific pursuits with the military service; and for the time he abandoned his intention of deserting the corps.
THE ORDNANCE SURVEY.
That the general reader may appreciate the services of Thomas Drummond in the sphere of duty which he now entered, it is necessary to explain briefly the principal operations in geodesy, and to glance at the history of the Ordnance Survey of Great Britain, and the methods which, up to his time, had been employed in it.
Geodesy, as a practical art, falls into two main divisions, in each of which there are peculiar difficulties to be surmounted: the first of these regards the measurement of base-lines; the second, the triangulation of the surface to be surveyed and measured.
A base-line is an initial measured line, whose length is assumed as the unit to which all other distances calculated in the survey are temporarily referred. The exact length of the base in yards, feet, and inches being known, these other distances admit at once of being reduced to yards, feet, and inches. error in measuring the base must enter into all of them. For convenience in measuring any large tract of country—in other words, in constructing a Trigonometrical Survey—it is necessary that the length of the base should be a considerable multiple of the standard unit of length, several thousand yards at least ; and for the accuracy of the survey, it is necessary that this length should be measured most exactly.
In measuring a base-line it is necessary to level the ground, to define the line, by marking in a permanent way its two extremities, and to allineate it-i.e., make it so straight as to allow of its being foreshortened to a point. These things being done, the line must be measured with some measure, or instrument of definite length. The measure should possess several qualities, to give any high degree of exactness in the measurement. It should be (1.) as large as is consistent with its being easily manageable ; (2.) of invariable length ; (3.) so formed as to allow of its being easily kept throughout its length in the line to be measured; and (4.) so formed as to allow of the exact juxtaposition of end to end of the duplicate measures employed, if such juxtaposition be not by some contrivance rendered unnecessary. It is obvious that the errors of measurement, supposing the measuring apparatus itself to be perfect, are apt to increase with the number of times that the measure must be applied to the base to go over its length; and that if the measure expands with heat and contracts with cold, or expands with moisture and contracts with dryness, like a rod of wood, the result of the measurement must be uncertain, and may be erroneous. If, again, the measure be flexible, like a long rod or chain, there must be difficulty in keeping it fully stretched, straight along its length, and wholly in the line; and errors corresponding to this difficulty must be entailed on the measurement.
The base being measured, the next set of operations, those of the triangulation, commence. Some object is fixed upon, which is considerably farther from either end of the base than the length of the base-line. Theodolites, with delicately graduated circles, capable of measuring angles to an extreme nicety, are then