easy distance of the survey office, which was established in the old Mountjoy barracks.
Under Colby's personal superintendence the organisation of the survey steadily developed, and the attempt to substitute speed for accuracy having been finally abandoned in 1832, the work began to progress more satisfactorily. In May 1833 the publication of the first Irish county— Londonderry—in fifty sheets, took place. Other counties followed in quick succession, so that on the completion of the map in 1847 there had been issued 1,939 sheets, surveyed and plotted on a scale of six inches to the statute mile, and which in the completeness of the details, the elaborate system of check and counter-check applied to them, and in harmony of artistic style and finish, far surpassed anything of the kind before produced. The amount of work involved in their preparation is indicated by the fact that from 1828 to the completion of the Irish survey in 1846, the average force employed thereon was twenty officers, two hundred sappers and miners, and two thousand civilian assistants, the expenditure during that time amounting to 720,000l. After he had got his system into working order, and finished maps were annually completed to the extent of two million to three million acres, Colby, as the ordnance records prove, did not hesitate year after year to take upon himself the responsibility of exceeding by large sums the votes sanctioned by parliament, rather than diminish the rates of expenditure and progress by discharging qualified assistants. To keep down the current expenditure, Colby for some time did not draw his own salary. When he subsequently applied for the arrears, they were refused and never paid. That the scientific accuracy on which Colby so strongly insisted was, in the highest sense, utilitarian and economical in its results, is shown by the following passage in the 'Annual Report of the Royal Astronomical Society' for 1852-3 (p. 16): 'It (the Irish map) has formed the basis of the poor-law boundaries in detail, determining the localities called electoral divisions, according to which the poor-law assessment is made; it has served for the poor-law valuation, which includes tenements, and which is distinct from the town-land or general valuation of all Ireland; it has been used as a means of obtaining an accurate annual return, at a very small cost, of every variety of agricultural produce in Ireland; it has been made the basis of the Irish census, and employed in the sale of property, the boundaries of fields and farms sold being laid down on the map and accurately coloured, and each map subsequently "enrolled," so that at any future time the property sold can be traced on the map, and from it identified on the ground; it has further been employed in carrying out the provisions of the Land Improvements Act; and last, but not least, it has greatly facilitated the task of carrying on in the most economical manner the various engineering works executed in the country.'
To these results thus achieved must be added a very complete series of tidal observations, made under Colby's direction during the progress of the survey, at twenty-two different stations round Ireland, and extending over a period of two months. The astronomer royal, in a paper on the 'Law of the Tides on the Coasts of Ireland,' based on them, observed: 'The circumstances of place, simultaneity, extent of plan, and conformity of plan appear to give them extraordinary value, and extent of time alone appears wanting to render them the most important series of tide observations that has ever been made' (Philos. Trans. 1845, p. 1). When Colby commenced the Irish survey, there was, strictly speaking, no topographical staff. At the close of the survey all branches of the work had been organised in one harmonious whole, and the country was in possession of a topographic corps composed of engineer officers, sappers, and civilians, which was, and has continued, second to none in the world. Among other improvements introduced by Colby during its progress may be mentioned the now familiar process of electrotyping, whereby the maps can be reproduced from duplicate plates without wearing out the originals; the introduction of contours or equi-distant level lines on the six-inch maps, the feasibility of such an undertaking at moderate cost having been previously ascertained by experiment in the barony of Ennishowen; and the training of picked men of the sappers and miners (now royal engineers) in the use of the larger instruments, whereby the services of an extra number of good geodesical observers (with whom strong sight and steadiness of hand are the chief essentials) were secured to the country at small cost. In 1833 Sir Henry, then Mr. De la Beche, suggested the preparation of a geological map of the west of England, which, after some deliberation, was entrusted by the government to Colby in conjunction with the projector, the ordnance finding the funds and engraving the maps, and Mr. De la Beche being answerable for the accuracy of the geological details placed on them. The arrangement continued in force until 1845, when the geological survey was transferred to the department of woods and forests. With this exception, and the publication of the sheets of the one-inch
