The requirements to be met were as follows: The apparatus was to be used by men whom by nature of their employment it was impossible to train individually, therefore its ignition must be simple and at the same time certain and quick in action, and carried on the float itself; a chamber had to be provided in which to as it were accumulate the smoke generated, which chamber had of necessity to have holes through which the smoke could issue. As the float had to be dropped after ignition from the deck of the vessel into the sea, and would consequently be submerged for a short time, these holes must be in some way sealed until the float rose to the surface. The pyrotechnic compositions which produce the greatest volume of smoke were found to take some considerable time to attain their maximum of production, and separate units had to be included which would develop almost instantaneously a big mass of smoke, pending the generation of the main supply. In addition, the float must be so constructed as to remain efficient when stored on the deck of a merchant vessel in all weathers and conditions. Two hundred thousand of these floats were issued during the war. The subject of smoke is one which naturally attracts the attention of the pyrotechnist, although in what might be called a negative direction. For display work the elimination of smoke is obviously of greater importance than its production, but inquiry into the one of necessity leads to a knowledge of the other. In some few cases the smoke generated is of value in adding to the effect of the burning composition; the most noticeable case of this is the use of coloured fire as flares, that is to say, burnt in masses for the illumination of trees and other natural features. Some years ago Messrs. C. T. Brock & Co. spent considerable time in eliminating as far as possible the smoke from coloured fire, when it was found that without the smoke the result was very poor. It was the reflection of the colour on the smoke upon which the illumination depended for its effect. This, however, is hardly germane to our subject, but is mentioned to indicate how largely the question of smoke enters into the work of the modern pyrotechnist. Commander Brock had, apart from his ordinary work, been engaged for some months prior to the outbreak of war on the question of the production of smoke for the Admiralty, and had also interested himself in the subject for commercial purposes, such as insecticide and other uses. He was therefore in a position, when the demand arose for smoke both for naval and military use, to start research in the matter considerably ahead of other inquirers, and to produce immediately a smoke that would supply the needs for the time being until more satisfactory means could be evolved.