Progress of Invention. 153 



but he preferred a mixture of charcoal and graphite, as not in the 

 least hygrometric. Mr. Gale uses powdered glass. When an equal 

 quantity of this is mixed with gunpowder, the explosion resembles 

 that of a squib, and the effect is nearly the same when one part 

 gunpowder and two parts glass are used. Three parts glass entirely 

 prevent explosion ; and, with four parts, even a red-hot poker pro- 

 duces no effect. When unprotected gunpowder is exploded in the 

 midst of that which is protected, the latter is merely scattered. M. 

 Piobert used only enough of the foreign substance to prevent the 

 gunpowder from being dangerous. The objections against any pro- 

 tective medium are serious ; the comparative cheapness of carriage 

 with non-explosive powder would, no doubt, compensate for its 

 greater quantity ; but the processes of mixing and sifting would be 

 dangerous, and in many cases objectionable ; unprotected might be 

 fatally mistaken for protected powder, and the very process of mix- 

 ture would most probably cause a deterioration which could not be 

 permitted. The project, on the whole, appears to be one of those 

 which are extremely plausible only until carefully examined. 



Nitroglycerins. — This highly explosive compound has been 

 lately applied, by M. Nabel, a Swedish engineer, with great success, 

 in mining. It was discovered in 1847 by M. Sobrero ; but until 

 now was not applied to any useful purpose. It is far less costly 

 than gunpowder, though four times stronger. It requires no tamp- 

 ing, and may be used where, on account of the dissipation of the 

 gases produced by the explosion of gunpowder, the latter would be 

 ineffective. When the hole formed in the rock is sufficiently deep, 

 any fissures which may have been discovered in connection with it 

 are to be stopped with clay, to prevent the escape of the nitro- 

 glycerine. The latter may then be poured in, and after it water, which 

 will float on its surface : a slow-match, having a percussion-cap at 

 the end, is next introduced into it. During some experiments that 

 were made in blasting a dolomitic rock, a litre and a half of 

 the nitro-glycerine, placed in a hole seven feet deep, and ten from 

 the outer face of the rock, produced two great fissures, one fifty 

 and the other twenty feet long ; and three-quarters of a litre, in 

 another case, poured into a similar hole, threw down about one 

 hundred cubic metres of the rock. With nitro-glycerine, the ex- 

 pense is only one-half as much as with gunpowder, to produce an 

 equal effect. 



Electricity the Cause op Animal Colours. — M. Nicolas 

 Wagner has recently brought before the Academy of Sciences 

 experiments which seem to show that electric currents are the cause 

 of the colours, at least of some animals. These experiments 

 were made on the nymph of a species of diurnal butterfly 

 (Vanessa urtica). Electric currents changed the reds into orange, 

 and the blacks into red ; and the most feeble current, especially if 

 from a constant battery, produced black spots, the shape of which 

 had a relation to the current. He ascertained, by means of an 

 extremely sensitive apparatus, that not only does electricity modify 

 and even produce colours, but that those found in the butterfly are 



