The first edition Of this number Of Van Nostrand's Science Series having become exhausted, it became necessary, in order to keep the series complete, to issue a new edition. But in the fifteen years which have elapsed since the appearance of the first edition, many changes have taken place in the views regarding the phenomena of explosions, and many new explosives have attracted the world's at tention, particularly the important class of smokeless powders. Therefore, since the theory advanced by Berthelot no longer accounts for all the known phe~ nomena, it was deemed best by the pub lishers to have the entire number re written.