diameter by the loop /, and No. 2 following it, occupies the focus. The support t, being immediately released, returns by the action of a spring to its former position, retains No. 2, and suffers No. I to escape through the loop into the cistern. "The wire a, b and the support revolve together, and carry round the focal ball, which is ignited as in fig. I by the two jets ≈, 2. These jets, which are movable round the joints d, d, enter through small apertures cut in the sides of the reflector, and are easily adjusted to the proper distance from the ball. "Wherever the light is required to be diffused equally around, the renewal of the lime may be effected still more easily by using a cylinder as represented in fig. 5, instead of a ball, which being gradually raised while revolving, brings fresh portions in succession opposite the jets. In a reflector, a cylinder occasions partial shadows at the top and bottom; still, however, the simplicity and certainty with which it may be renewed will probably entitle it to a preference even in this case. "The apparatus for supplying the lamps with gas is represented in fig 6. It consists of two strong cylinders, A, 3 feet high, the one for oxygen, the other for hydrogen; the gas is compressed two or three times in each, the latter by being generated under pressure, the former by being pumped in. To each of these gas-holders a governor, B, is attached, of one of which a section is shown, by which means, whatever be the variation of pressure in the gas-holder, provided it exceed that of the governor, the gas will issue at x with a uniform and constant stream; in the present instance under a pressure of 30 inches of water. . . During the winter of 1829 and the spring of 1830 experiments were tried under the directions of Trinity House, and upon one occasion, before the apparatus was in per fect working order, an explosion took place. Drummond's sister, on hearing of the accident, wrote warning him to be more careful in future. He replied playfully: DRUMMOND TO HIS SISTER. "LONDON, January 16th, 1830. "MY DEAR ELIZA,-A week, more than a week, has passed since I ought, and since I intended, to have answered your kind, kind letter; but every day and every evening has brought such constant occupation that I positively have not had time. "The consequence, no doubt, has been many conjectures and much exercise to my dear mother, if the bell rang about post-time. Now, what have been your conjectures? Another explosion, perhaps, and the heir-presumptive,1 along with all my beautiful apparatus, sent to the upper, or perhaps the under regions; or everything gone off well, and the Duke extremely delighted, expressed himself highly gratified, and intended conferring upon me some signal mark of his royal approbation! Well, to keep you in suspense no longer. The Duke was not present; he was unwell, and unable to leave his house. We were all prepared, for the messenger did not arrive till the last moment. The next Board day, when he is expected, is the 5th February. Meanwhile, we proceed with the experiments, and it is with them that I have been so much engaged this week. But this is Saturday evening, an evening of repose and enjoyment, and I have taken advantage of it to discharge my debt to you. I was grieved to hear of more colds and plasters, and I fear much that this fierce weather does not agree with you. . . . "Do you ... ride? How is the pony? Has John re 1 The Duke of Clarence, afterwards William IV., who, in his character of Master of the Trinity Corporation, was expected to witness the experiments. -McLennan. you. covered, and has he been laying down the law? I think you might manage among you to write a little oftener. There are some long gaps in our correspondence, and some long intervals during which I hear nothing of Almost all my acquaintances have been ill, more or less. I have great reason to be thankful that I have been so well; indeed, notwithstanding all my work, I am in rude health, sleep but one sleep, and no palpitation. All the advice you gave me in your letter I acknowledge to be excellent, yet the exhibition was unavoidable, and so was the explosion. But I think they have got over it; if not, I will tell them the first time I have an opportunity of making a speech, that if I had been making an experiment before men unacquainted with the peculiar nature of such experiments, I should have declined proceeding under such circumstances; but before enlightened and intelligent men, whose indulgence and partiality I had more than once experienced, I could have no hesitation in trying even a first experiment, deeming it the best compliment I could pay them to show them the apparatus under the most disadvantageous circumstances. . . . My best and kindest love to you all at home.—Adieu, my dearest Eliza, and believe me, your affectionate brother, "T. DRUMMOND.” In May 1830 the light was exhibited at the temporary lighthouse, Purfleet, and we have a graphic account of the experiment from Captain Basil Hall, R.N., in a letter to Drummond. Captain Hall witnessed the exhibition from the Trinity Wharf, Blackwall, a distance of 10 miles from Purfleet; and among the observers with him were Sir George Cockburn and Mr Barrow from the Admiralty, the Lord Advocate of Scotland, Sir Thomas Brisbane, Colonel Colby, Captain Beaufort, hydrographer to the Admiralty. Captain Hall wrote: |