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cess as a man of science, had he desired it, must have been of a very distinguished kind. A strongly characteristic feature of Mr Drummond's scientific undertakings and improvements was, their eminently practical nature, and the directness with which they attained the distinct object in view, by means highly ingenious, and quite out of the common line of contrivance, yet meeting, fully and precisely, every exigency of the case.
The scene of his scientific labours was the Irish Survey, one of the greatest national works of this description which was ever undertaken. In the very outset of this undertaking great difficulties were experienced, owing to the magnitude of the triangles to be formed, and the dreadful weather encountered, which for weeks and months together rendered the stations invisible from each other.
On occasion of a similar difficulty, but on a smaller scale, during the remeasurement of some of General Roy's triangles, the heliostat of Gauss had been used with effect, but the apparatus devised by its inventor not being obtainable for directing it properly, the resources of Mr Drummond readily furnished, by a simple and very ingenious contrivance, the means of doing so.*
But the difficulties of the Irish operations were of a higher kind, and it became further necessary to provide some still more powerful means of producing a light which should penetrate 60, 70, or 80 miles of mist and drizzle, preserving a concentration and sharpness sufficient for a point of astronomical observation. On this occasion was produced the celebrated “Drummond Light,” in which a small ball of quicklime, intensely heated by the flames of spirit lamps, urged by jets of oxygen gas concentrated on it, pours forth a flood of splendour like the meridian sun, insupportable to the eye, and when enclosed in its proper reflector, casting broad shadows at a distance of many miles.
The fact that lime intensely heated gives out a brilliant light, was not new. Not to speak of a strange plan for producing intense heat by addition of much lime to little fuel, which
had been propounded in a plan whose failure might have been certainly predicted, and which argued the observation of a vivid apparent ignition originating in the heated surface of the lime, Sir David Brewster had noticed that small points of wood dipped in a solution of lime, and arranged around a candle, so as to touch the outer invisible flame in which the heat resides, gave out a copious and very white light, and proprosed this as a mean of increasing the power of light from candles.*
The merit of Mr Drummond in this invention is of a different kind, and consists in the ready seizure of fact precisely bearing on his own case, and its perfectly effective application to a particular object in view.
It is now with a melancholy pleasure that I recall the impression produced by the view of this magnificent spectacle, as exhibited (previous to its trial in the field) in the vast Armoury in the Tower, an apartment 300 feet long, placed at his disposal for the occasion.
The common Argand burner and parabolic reflector of a British lighthouse was first exhibited (the room being darkened), and with considerable effect. Fresnel's superb lamp was next disclosed, at whose superior effect the other seemed to dwindle, and showed in a manner quite subordinate. But when the gas began to play, and, the lime being now brought to its full ignition, the screen was suddenly removed, a glare shown forth overpowering, and as it were annihilating, both its predecessors, which appeared by its side—the one as a feeble gleam which it required attention to see, the other like a mere plate of heated metal. A shout of triumph and admiration burst from all present. Prisms to analyse the rays, photometric contrivances to measure their intensity, screens to cast shadows, were speedily in requisition, and the scene was one of extraordinary excitement.
The new light succeeded perfectly for the object of its invention. The azimuth of Slieve Snaght (one station) as seen from the Divis hill, at a distance of nearly 70 miles, was obtained by
* See Appendix II.
its help under circumstances of uncommon difficulty; and, if I mistake not, the coasts of Ireland and Scotland were connected by an immense triangle, the one apex resting on Knocklach, the other on Ben-Lomond, 95 miles miles distant, by the same powerful means.
Mr Drummond proposed this light as a means of illuminating lighthouses, and experiments were made to ascertain its applicability to that purpose.
So far as the illumination goes, the success was complete, the effect surpassing everything that had been before attempted. An account of these experiments will be found in the Transactions of the Royal Society.
The exigencies of the Irish Survey were continually calling into full activity the energies of all employed in it. I am unable decidedly to say, and will not therefore incur the hazard of doing injustice to the talented and estimable officer at the head of that operation, by deciding whether the beautiful and simple idea, by which was performed the compensation for temperature of the rods employed in measuring the base in the plains near Londonderry, originated with himself or with Mr Drummond. It proved as successful in practice as it is perfect in theory, and in its effects went to abolish altogether one of the most precarious and annoying corrections in that most delicate and difficult geodetical operation.
To whichever be due the credit of originating this invention, the details of the contrivance and execution of the project devolved on the latter, who, in accordance with what seems to have been a constant principle in his conduct, to leave nothing undone that personal exertion and assiduity could accomplish to ensure success, not content with entrusting, as many would have done, the adjustment of the compensation to an instrument maker, himself executed, in the midst of furnaces, ovens, and freezing mixtures, all the trials, manipulations, and measurements, necessary to ensure success.
An anecdote may be mentioned here which sets in a strong light this leading principle of hearty devotion to his object and its duties, not only to the exclusion of personal ease, but to the atter abnegation of all that egotistical feeling which
induces so many to turn aside from the suggestions of another with indifference, if not with aversion. While engaged in these operations, the conversation between himself and a scientific friend happened to turn on the discovery of Mitscherlich, who had shown that in certain crystallised substances heat occasions expansion in some directions, and contraction in others, necessarily implying invariability in some intermediate directions. It was suggested, as a bare possibility, that such a condition might be satisfied by cutting mica in some certain direction to be ascertained by trial, in which case an inexpansive or naturally compensated measure would be obtained. The hint held out but little promise. Nevertheless, some time afterwards, the writer of these lines, happening to visit him in his apartments at the Tower, found him surrounded by stripes of mica, and busied in working out the suggestion. The result, however, proved abortive in everything but in the illustration of character it afforded.
In the active operation of the Irish Survey he maintained on all occasions the character of a consummate observer, and most able and active coadjutor. In remote and rural districts, surrounded by a peasantry often prejudiced, sometimes distrustful, generally superstitious, much care and all the arts of conciliation were requisite to secure their aid, and even in some cases to avert their ill offices. It may easily be imagined in such a service how important were the advantages of a temper eminently conciliatory, and which secured on all occasions the willing and joyful aid of every one connected with or subordinate to him. Every one, indeed, was not only willing but eager to work in conjunction with him, and felt it as a privilege and a pleasure to do so.
I am not enough acquainted with the railway proceedings to give any account of his labours on that subject. Indeed, in what I have above said, I have confined myself to such points as I have a clear recollection and personal knowledge of; but if, from what I have said, any extract may appear worthy of being put forward in any way, you are at liberty to make any use of it you may think proper. And in conclusion, I beg you will accept, my dear Madam, the heartfelt condolence of one who sincerely esteemed and admired him you have lost, and who would gladly have cultivated his more intimate friendship had circumstances thrown us more together.-I remain, dear Madam, your very obedient servant,
J. F. W. HERSCHEL.
No. II. The proposal of Sir David Brewster, referred to in Sir John Herschel's letter, is the subject of a short paper by Sir David, in the “Edinburgh Philosophical Journal” for 1820, which merits quotation as illustrating the early stages of discovery in connection with the Drummond Light :
"About the middle of last summer, Mr Cameron of Glasgow (the inventor of the ingenious method of making crucibles, described in our last number), brought me some pieces of wood that had been steeped in oxymuriate of lime, the common bleaching powder of Mr Tennant, and mentioned to me that he had observed a singular luminous property in the white substance which remained after burning the wood. In order to observe this appearance, the end of the piece of wood is held in the flame of a candle till it is completely burnt. A sort of white substance is left at the end of the wood, and when this substance is held in the outer part of the flame of the candle, it exhibits a brilliant dazzling light, not much, if at all, inferior to that which arises from the deflagration of charcoal by the action of galvanism. When bits of woods of different kinds were steeped in the oxymuriate of lime, they gave the same results, only the harder woods seemed to produce a more satisfactory effect than the softer kinds.
“By submitting the whole substance to the action of the blowpipe, I found that the intensity of the light was greatly increased, but the white substance was generally driven away by the blast.
“Upon showing this experiment to Mr Sivright of Meggetland, he conjectured that the white residue of the burnt wood consisted of particles of lime in a minute state of division; and