At this period of invention and improvement which preceded the commencement of the survey of Ireland, Mr. Drummond gave some consideration to the barometer, an instrument even now susceptible of improvement, but which had not then received so much attention as it has since. His favourite construction was the siphon, and he made one with his own hands, which performed remarkably wall; but he was not in possession of various modes of reading which have since been used: and he devised a singular mode of bisecting a reflected image of the surface—a ghost, as he called it ; but he arrived at no permanent or practical result, and at length abandoned the subject from a conviction, to use his own words, that the errors to which the barometer was liable from causes beyond control, were greater thau the quantities ha had been dealing with. His researches on light, and his intimacy with Professor Leslie, led him to the use of the photo meter, the aithroscope, and other philosophical instruments of more or less practical utility—among others, Wollaston's thermo-barometer ; indeed, at this period so active was his mind and so constant his application, that scarcely an instrument existed that he did not examiue and consider, with a view to render it useful for the purposes of the survey ; and the elaborate collection with which the meteorological observatory on Divis was furnished, presented a singular spectacle on the mountain-top. He carefully made observations and recorded them, till a calamitous storm destroyed the observatory and all its contents together.
A severe illness which Mr. Drummond contracted from exposure daring the Irish survey compelled him to return to Edinburgh, where ha was unable to devote himself to study, but he had taken much pains to perfect his light, and he now began to revert to the idea that he had early formed of adapting it to lighthouses. In this he was liberally met by the corporation of Trinity-house, and to it he devoted much of his time during the following winters : the experi ments he made, with their success, are detailed in the 'Philosophical Transactions' for 1830. The corporation of Trinity-house placed at his disposal a small lighthouse at Purfleet ; and the brilliant effect of the light as seen from Blackwell, where at a distance of ten miles, it was sufficiently strong to cast shadows, made it an object of very general interest. With regard to his share in the application it may be proper to remark, that Mr. Drummond's merit was in rendering
practically useful a recondite experiment,—by devising a means of procuring and using without danger agents so turbulent as the mixed gases, making the apparatus sufficiently portable and simple to be employed in the circumstances of exposure required for the survey, and, perhaps more than all, for the happy idea of using this minute spherula of concentrated light as the radiating focus of a parabolic mirror. But the original object of the lamp, its application to light houses, presents difficulties which have yet to be overcome: The abstrac tion of Mr. Drummond's attention at the moment when he was nearest to success, must, so far as the light is concerned, be considered matter of regret.
Mr. Drummond was employed to superintend the very laborious operations necessary to the perfecting the schedules and laying down, the boundaries to the old and the new boroughs under the provisions of the Reform Bill. Mr. Drummond was appointed to this commission on the recommendation of Lord Brougham, not however without some severe opposition from one of his colleagues, who doubted much as to the propriety of putting at the head of so important a depart ment a young lieutenant of the Engineers. He however more than justified the expectation formed by his patron.
When the Reform Bill was passed, Mr. Drummond returned to his duties on the survey, and he had made preparation for giving an account of the base before adverted to, when he was again called into public life by being appointed Lord Spencer's private secretary. On the dissolution of the government he received a pension of 300/. a year, obtained for him by Lord Brougham, his constant friend.
In 1835 he was made under-secretary for Ireland; he much dis tinguished himself in the report on railways in Ireland, being at the head of the commission. We shall not attempt to trace his labours as a politician or on the railway commission, but his talents and assiduity were admitted by all, even his strongest political opponents. lie laboured incessantly at his duties, and probably hastened his death by his continued application. This took place April 15, 1840, " in the plenitude of mental power and maturity of knowledge, beloved in private and esteemed in public." Soon after his death there was a subscription for a statue, which was executed at Rome, and erected in Dublin.