82 ANNUAL OF SCIENTIFIC DISCOVERY. 



the collier in dangei'ous places ; but, undei* the onlinaiy condi- 

 tions, it has not been Ibund practicable to employ it. Dumas and 

 Benoit propose to apply lliiumkorff 's coil machine and Geissler's 

 tubes; to use, indeed, those tubes, with their beautilul auroral 

 light, as a miner's lamp. 



The tube, it is now generally known, is fdled with some highly 

 rarefied gas, and platinum Avires are hermetically sealed into tlie 

 ends. AVhen tiie discharges Irom a Rliumkorir's coil apparatus 

 are passed through this tube, it becomes filled with a mild, difl'usive 

 light, which lasts as long as the discharges pass through the rare- 

 fied medium. This light is unaccompanied by heat; it cannot, 

 therefore, under any circumstances, explode the fire-damp of our 

 coal mines. 



This new " safety lamp" consists essentially of a cylindrical zinc 

 vessel about six inches high and four inches in diameter, which 

 encloses a porous vessel holding a cylinder of carbon. A solution 

 of the bichromate of potash is placed within the ])()rous cell, and di- 

 lute sulphuric acid without it. This battery is secured by a wooden 

 cover, which is, by means of India-rubber packing, made to fit 

 closely. Then there are a Rhumkorfl"'s coil and condenser, and a 

 Geissfer's tube. This tube is arranged into a conical coil, so that 

 a large surface of light is secui*ed within a small space. Of course, 

 the oijjection to this will be the cumbrous character of the machine 

 and its adjuncts. Dumas and Benoit think tlu^y have answered 

 this objection by the very ingenious arrangement which they have 

 secured. We are assured that the weight of the glass case does 

 not exceed two pounds, and that of the other parts of the appara- 

 tus is not more than twelve pounds. That there are many advan- 

 tages in this electrical lamp cannot be denied. But we doubt if 

 so delicate a machine can be entrusted to the hands of colliers. 

 Under circumstances of danger, such a lamp as this would jjrove 

 of the highest value. As Dumas and Bcmoit are making practical 

 trials of their "cold light," as they call it, we shall, if they are 

 successful, hear more of this interesting^ipplication. 



The Institute of France has given the inventors a pi-ize of one 

 thousand francs for the ingenuity of their jilan. We understand 

 that some trials have been made in the Newcastle collieries. The 

 ol)jection raised by the miners is, that the light is a "glimmer," — 

 not a steady illumination. — Reader. 



HYDRAULIC 3(L\.CHINE FOR CUTTING COAL. 



This machine, by W. E. Carratt, has now been at work for two 

 years. It does not dispense with labor, but it performs the under- 

 cutting, which was a most laborious operation, either in the end 

 or face of the coal, in a more efficient and economic manner 

 than the miner can do it himself. By it the size of the coal is im- 

 proved, the amount of slack reduced, and a single seam will 

 jdeld more by one thousand tons of coal per acre, than when 

 worked by hand-labor. The machine undercuts its "holes," or 

 "kirves," with one man and one boy as attendants, and comi^letes 

 the work, with once going over, at the rate of fifteen yards i^er 



