The writer was an eminent chemist. He expressed the opinion that the one possible means of success was the use of a power which, as in the case of explosives, could be easily produced from substances of comparative light weight. He urged, it was only of late years that any real knowledge of the nature of explosives was obtained. It was nearly four hundred years after the discovery of gunpowder before any possible substitutes were invented. It was again a long time before it was discovered that explosives partook of two distinctly separate characters. One was the quick or shattering compound producing instantaneous effect; the other was the slow or rending compound of more protracted action. He dwelt on the fact that in all cases the force yielded by explosives was through the change of a solid into a gaseous body, and that the volume of the gaseous body was greatly increased by the expansion consequent on the heat evolved during decomposition. The total amount of heat evolved during decomposition did not differ, but evidently the concentration of heat at any one time depended on the rapidity of the decomposition. The volume of gas, independent of expansion by heat, varied also with different substances. Blasting oil, for instance, gave nearly thirteen hundred times its own volume of gas, and this was increased more than eight times by the concentration of heat; gunpowder only yielded in gas expanded by heat eight hundred times its own volume: or, in other words, the one yielded through decomposition thirteen times the volume of the other. He went on to argue that what was required was the leisurely chemical decomposition of a solid into a gas without sensible explosion, and of such a slow character as to avoid the production of great heat. He referred, as an example of the change resulting from the contact of two bodies, to the effect of safety matches. The match would only ignite by contact with a specially prepared surface. This match was as great an improvement on the old primitive match, as would be a decomposing material the force of which could be controlled, an improvement on the present means of obtaining power. He expressed a positive opinion that substances could be found whose rapidity of decomposition, and consequent heat and strength, could be nicely regulated, so that a force could be employed which would not be too sudden nor too strong to be used in substitution of steam or compressed air. He was, moreover, of opinion that, instead of the substances being mixed ready for use, with the concurrent danger, a mode could be devised of bringing the different component parts into contact in a not dissimilar manner to the application of the safety match, thereby assuring absolute immunity from danger in the carriage of the materials. This discovery could be made, he went on to say; and upon it depended improvement in aerial travelling. Each fan could be impelled by a separate machine of a light weight, worked with perfect safety by a