At the close of the year a party of the corps was attached to Captain Drummond to assist him in carrying on experiments and observations with his lamp and heliostat. The observing station was on Divis Mountain, near Belfast, and the season was fearfully inclement. Frequently the mountain and the camp were enveloped in snow, and the blowing of a keen cold wind made their situation anything but agreeable. On two or three occasions a storm visited their desolate location, and carried away in its blast, tents, baggage, and stores. Still the men were sturdy in frame, willing in disposition, and exerted themselves in the discharge of their duties under trials of no ordinary character. A few men of the party, thirteen in number, were removed to Slieve Snacht in Donegal, to exhibit the light, that it might be observed from Divis. The distance between the heights was sixty-six miles. The camp on Snacht was at an altitude of 2,000 feet, and the party peculiarly exposed. Few in number, they were ill able to buffet with the tempests of those cold regions; “and the tents were so frequently blown down,” and had become so shattered and torn, “that, after the first few days, they abandoned them, and constructed huts of rough stones, filling the interstices with turf.” On this bleak mountain the success of the light was first proved. At night the lamp was directed on Divis. It was then dark, and both the camps were covered with snow. The wind blew piercingly over the mountain tops, and almost flayed the faces of the men as they worked. But it was on that stormy night that the light, first seen by the sapper sentry, “burst into view with surpassing splendour,” and afterwards became one of the most useful agencies in the prosecution of the survey.[251] ----- Footnote 251: ‘Prof. Papers,’ iv.; preface, pp. xiv. xvii. -----