it seems quite impossible to maintain a steady light of this splendid description for the purposes of the coast. The heat of the united flames of these gases is so intense that any substance yet applied to them is apt to be suddenly destroyed, and even platina, the most infusible of the metals, quickly melts before it. It is from this circumstance chiefly that the difficulty of making practical use of this light arises. ... Important advantages might doubtless be obtained by using this light during hazy weather, and the reporter1 is resolved to spare no pains on his part to bring about its introduction into lighthouses. When the reporter looks back to his early trials with coal gas, which he believes he was the first to exhibit in an experimental form in Edinburgh, and contrasts the conceptions formed by himself and others regarding its general application to economical purposes, with the ease of managing it at the present day, he does not despair of the Drummond light being made applicable to lighthouses. All other lights seem, in any comparative view of intensity, to sink into insignificance; and this light approaches, in its properties, more nearly to solar light, than any other produced by artificial means.”2

Finally, the Committee reported—

"[Lieutenant] Drummond stated to the Committee all the objections to the present use of his light in lighthouses; but your Committee are so strongly impressed with its importance, and with the merits and ability of Lieutenant Drummond, that they recommend that means should be adopted without delay for prosecuting still further the experiments recommended by him, and under his direction if possible; or if he cannot superintend them, then under some other fit person."

1 Mr Stevenson made a special report on the light.

"Parliamentary Papers," Vol. XII. for 1834, Appendix, p. 117. ย Ibid., Report, p. xxxiii.

But while the fate of the light was yet uncertain, and even when success seemed near at hand, Drummond glided into politics, and, in fact, abandoned the invention. This new departure of Drummond, at the crisis of his career as an inventor and a scientist, General Larcom has, in an eloquent passage, deplored. He says, "This abstraction of Mr Drummond's attention at the moment when he was nearest to success, must, so far as the light is concerned, be matter of regret; with its projector it has dropped; but if it be practicable, ingenuity will, doubtless, sooner or later, be directed to render it available, and the Drummond light may yet cheer the home-bound mariner from the Great Skelley, or the Tuskar." 1

Two other inventions, which were used in the Irish Survey, deserve to be mentioned. They were a heliostat, designed by Drummond; and measuring bars, designed by Colby, and executed by Drummond.

In the paper published by the Royal Society in 1826, Drummond described the heliostat.

"[Plate III.,] fig. 1, represents [the instrument]; ab is a telescope of twelve-inch focal length, and serves as the axis of the instrument; the bars bd and be form a right angle; and the bar gg, placed so that bf (fig. 2) shall be equal to fg, works between bd and bc, carrying a small telescope such as is usually attached to sextants, and provided with a rectangular eye-piece. The mirror mm, of which different sizes may be used, according to circumstances, is connected with the instrument by three adjusting screws r. The bars bc, and b'c', being now made to coincide with ab, a movable spirit-level is placed across them in the position

1 Memoir.

Dr Sullivan, President of the Queen's College, Cork, writes, under date April 1888: The Drummond light continues to be still used, though the name of the inventor is not usually associated with it. People speak of it generally under the name of the Lime Light,' the Oxyhydrogen Lamp,' &c." Letter penès me.

ll (fig 2), and rendered horizontal by the foot screws; by the same means the axis ab, to which a level is permanently attached, is also brought into a horizontal position. The movable spirit-level being now transferred to the surface of the mirror, the three adjusting screws r are employed to render it horizontal. The mirror will then be parallel to ab and I, and will have the required position on the instrument. The telescope ab being now directed on the object to which the reflection is to be thrown, and the small telescope gg turned towards the sun, its rays will be reflected parallel to the axis of the instrument ab. The head of the screw R (fig 2) is graduated, so that by means of it, and the spirit-level attached to the axis, the required elevation or depression may be given to the instrument when the object towards which it is directed happens to be invisible, its direction only being known relatively to some nearer object; and which, it may be remarked, has been the case in every instance in which it has been employed on the Survey. When packed for travelling, the mirror mm is detached, and the bar gg turned till it coincides with bf. The instrument once directed, its management was usually confided to one of the non-commissioned officers." 1

The measuring bars were an ingenious contrivance for measuring a base, and were first tried in the measurement of the base of Lough Foyle; the most accurately measured base in the world, according to Sir John Herschell. It was for some time uncertain what share Drummond took in the invention. But the matter has been cleared up by General Larcom. He writes :—

"My conviction with regard to the relative shares of Colby and Drummond in the design and execution of

1 66 Philosophical Transactions for 1826." Drummond improved the heliostat, so that the telescope was finally dispensed with. Larcom, Memoir, "Enc. Brit."

2 McLennan.