Of the mass of writing dealing with the subject, the work of two writers stands out prominently—the late Mr. Oscar Guttman in his "History of Explosives," and Col. H. W. L. Hume in his "Origin of Artillery," whose observations cover the field of information on the subject, although approaching from slightly different angles.
Neither, however, gives an exact explanation satisfactorily covering the projection of Greek or sea fire. Col. Hume, rejecting earlier theories, goes somewhat to the other extreme: he denies the knowledge of saltpetre before the twelfth century, but attempts to explain the phenomenon by the use of phosphide of calcium.
He premises four conditions to be filled by the weapon or apparatus. These conditions are fulfilled by the explanation already briefly touched upon on page 15, and the writer is convinced that this simple although apparently little known phenomenon is the true explanation of the terrible, mysterious Greek or sea fire.
If a mixture of saltpetre, pitch, and sulphur is charged into a long tube sufficiently strong and ignited it will burn, giving off dense smoke, for a short time, when it appears to choke momentarily. This choking is followed by a more or less violent outburst, which may be likened to a "cough," projecting a burning mass of composition to a considerable distance; the action is repeated with surprising regularity during the burning of the whole of the composition throughout the length of the tube, and will, the writer is confident, satisfy any unbiased observer that here is the true explanation of the phenomenon.
Let us see how the requirements mentioned by Col. Hume are fulfilled. The first, "It was a wet fire," i.e., its action necessarily connected in some way with water or the sea, and as a matter of fact it was used at sea with great success
