The difficulties to be encountered are doubtless sufficiently formidable. Gas, it is clear, could not be carried into a hostile country or into remote and nearly inaccessible districts. Even if procurable at all near the battle-field it could only be obtained by a long and difficult process of generation at the very time when speed and simplicity would be the main factors of success. Gas, therefore, being practically out of the question, it seems to have occurred to Mr. Spencer, the well-known balloon manufacturer, that it would be better after all to revert to the original conception of Montgolfier. The old-fashioned fire-ball, which acquired its power of ascension from rarefied air produced by burning straw or something similar, was, of course, of far too dangerous a character, and had been productive of far too many fatal accidents. It remained, therefore, to construct a balloon of some uninflammable material, in order to obviate this difficulty; and with the assistance of his friend, Mr. Fisher, the Secretary of the United Asbestos Company of London, he ultimately succeeded in so doing. A balloon was accordingly constructed, the whole of the lower part of which was formed of fine asbestos cloth, and the remainder of canvas, covered with a fireproof solution. The first trial took place in the grounds of the Welsh Harp, at Hendon, and this has since been repeated at Chatham, under the inspection of the Royal Engineers' Committee, and on both occasions, I am informed, with success. The balloon, which was a model only, stood about 30 feet high, and was suspended between two uprights, between which it hung down like a limp rag. It was of a cylindrical shape, having a deep zone at the equator, and a containing capacity of about 300 feet. Attached to the neck was a copper spirit-lamp. As soon as a light was put to the spirit the inflation commenced, and the balloon was fully distended in a space of about five minutes. The immense advantage gained by this method over the tedious and difficult process of inflation by gas, even under the most favourable circumstances, is sufficiently obvious, whilst it is at the same time apparent that the quantity of spirit requisite for an endless number of ascents could be carried about with the greatest facility. Another advantage remains to be considered, in that whilst the large volume of gas required for an ordinary balloon is in itself deleterious, the rarefied air in the new fireproof balloon is perfectly innocuous, and it can be raised or lowered at will simply by turning the neck of the lamp a little up or down. It is perhaps somewhat superfluous to say that the Russian Government at once adopted these balloons for war purposes.