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.

It is to be regretted 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; but at the moment the pressure on the survey, as regarded its more immediately practical results, was beginning to be felt, and it is not surprising that he found it necessary to devote his sole attention to the realization of the hopes of the public, by hastening on the more simple topographical work, and the preparation of the 6 inch maps, so urgently required for the use of the Valuation Commission. Yet, making this fair allowance for a first delay in publishing an account of the measurement of the base line, and also for the difficulties imposed upon Major Colby by the removal, first of Lieutenant Drummond, who was called upon by the Government to enter on those political duties which he so ably performed, first on the Reform Boundary Commission, then as Private Secretary to Lord Althorpe, and finally as Under-Secretary in Ireland; and again of Lieutenant Murphy, who was required to take charge of the scientific operations of the Euphrates expedition, under Colonel Chesney, R.A., as these two officers had been more concerned in the preliminary experiments and subsequent operations connected with the measurement than

any others, it must still be admitted that the protracted delay of so many years was due to a constitutional defect in Major Colby's character, as in him, that which in moderation would have been a theoretical virtue of a high order, became, in excess, a practical vice. Major Colby, in fact, thought little of personal distinction, and as he looked upon the publication of maps as the great object of the Irish survey, his attention became concentrated upon it, and, for a time, he almost overlooked that portion of his work which, though of comparatively less importance to the public at large, was the portion which would be most welcomed and appreciated by philosophers, and which was most fitted to elevate his character in their estimation. It was thus that whilst the townland survey began to move with giant strides, and to exhibit in all its movements an organization as perfect as that of the most admirably fitted machine, the remembrance of the scientific operations appeared to be gradually fading away into oblivion. Fortunately however the operations on the shores of Lough Foyle had been witnessed by too many men of science to allow them to remain barren of results; and soon afterwards Colonel Everest, then Surveyor General of India, being in England for the recovery of his health, applied to the directors of the East India Company for authority to order from Troughton and Simms a complete set of Major Colby's compensation bars for the use of the Indian survey, and with their usual liberality in all matters connected with

science, the directors immediately assented. The bars were made, taken to India by Colonel Everest, used in verifying several of the preceding measurements, and actually first described by him in his account of those operations. In a similar manner Mr. Maclear, the Astronomer at Cape Town, applied for the use of the bars made for the first survey, to measure a base in Africa, preparatory to the operations for verifying Lacaille's arc, and they were taken to the Cape for that purpose, in charge of the late Captain Henderson, R.E., who had been one of the officers employed in measuring the base on Lough Foyle.

Before, therefore, Major Colby had published any description, however brief, of his measuring apparatus, he had seen it described by another officer of eminent scientific abilities, and employed both in Asia and Africa, in verifying some of the most important arcal measurements which had ever been made, a practical triumph which was probably more congenial to the mind of Major Colby than any personal acknowledgment or testimonial would have been. At length, however, the omission was supplied, and, at the request of General Colby, an account of the measurement of the base on Lough Foyle, including a full description of the apparatus, was published under the immediate superintendence of Captain (now Lieut.-Colonel) Yolland. Though it is impossible not to regret that the inventor of the new measuring bars, and the conductor of the first measurement made with them, should not have pub

lished a work which describes inventions and operations so pre-eminently his own, yet, at the same time, the omission may be received as a powerful illustration of the total absence of selfishness in that remarkable man. So free indeed was he from that vice of little minds, and so ready on all occasions to recognize and give publicity to the merits and labours of his officers, that many people almost overlooked the commanding officer in their admiration of the subalterns; a feeling, indeed, so strong, that for a long time Lieutenant Drummond was even considered the inventor of the very compensation bars of which he had, at the first, disapproved. Captain Yolland had not himself taken part in the Irish survey, but he had for some years been the executive officer of the Ordnance survey, had superintended the numerous calculations necessary for the task he undertook, and by the able description of the measurement of the Lough Foyle base already alluded to, as well as by the excellent Treatise on "Geodesy," in the third volume of the Academy course, has proved his sound knowledge of the subject, and his ability to support the character of a great National Survey. To these two works my brother officers must refer for further information on subjects which I have here dwelt upon, only so far as was necessary for recording the labours, and delineating the character of General Colby.

The mental activity which was called into action at the commencement of the Irish survey was not exhausted in the one act of invention which has been

described. It became also a question whether the old theodolite should still continue the sole instrument for taking angles, or whether the "Repeating Circle," invented by Borda, and ever since the favourite instrument of Foreign geodesists, or some modification of it, should be adopted in place of the theodolite, or in association with it. In the great theodolite of Ramsden, the accuracy of the great divisions of a large circle of 3 feet in diameter, and the minute subdivision attained by delicate micrometer microscopes, were considered to be the surest means of obtaining accuracy of reading; whereas in the repeating circle, made comparatively small for the sake of portability, the errors of reading were sought to be compensated, or neutralized, by reducing the number of readings, necessary for several observations of the same angle, to two only. For effecting this purpose two concentric circles are used, capable of moving separately or being clamped together, the outer of which is graduated, and the inner carried the verniers and telescope.

In this arrangement the plane of the instrument, when connected with its stand, is brought into the plane of the observer and of the two objects to be observed, and the two circles being clamped together are turned round on the common axis, until the telescope wires bisect the left hand object, the vernier of the inner circle being either at 0°, or at some other definite degree of the outer circle: the outer circle is then clamped, and the inner, being unclamped, is turned until the right hand object is