The cause of these premature explosions was clearly investigated and keenly discussed, some years since, by several members of the Cornwall Geological Society, and an ingenious paper on the subject was written by the then secretary, Dr. Paris. He considered the ignition as invariably taking place by the sparks produced by the collision of the tamping bars (which, at that time, were generally made of iron), and the stony materials in contact with the powder, and proposed, as an infallible preventive, an alloy bar of tin and copper, which is incapable, under ordinary circumstances, of striking fire with stone. In the same essay, an improved mode of conveying the powder to the bottom of the hole was proposed. Both of these suggestions have been only very partially adopted, and their value, as preventives, has been very differently estimated by different practical men. A greater improvement than either of these has been adopted, of late years, in many mines, namely, the employment of soft tamping-stuff, incapable of yielding sparks on percussion.
With these various alterations, and with an increased degree of care and attention on the part of the superintendents, awakened and confirmed by the discussions above alluded to, the fact assuredly is, that accidents, from this cause, are much rarer of late years in the mines in this district.
The ordinary period of under-ground labour is six hours in the twenty-four; at the end of this time the labour is assumed by a fresh band from the surface, (or from grass, as the miners term it), who are, in their turn, relieved at the end of a like period. The dress of a miner, under-ground, consists of a coarse
