

RECENT PROGRESS IN PHYSICS. 



417 



Fi.'. 57. 



unsuited for every day use by common laborers, and, therefore never 

 was used to a great extent.* In consequence of the many fatal 

 accidents in mines and quarries, Roberts, of England, directed his 

 attention to this subject. After many endeavors he succeeded in 

 making the application of the galvanic current to blasting so simple 

 that his process deserves general commendation. It was first described 

 in the Mechanics' Magazine, May, 1842, p. 353. — (Dingler's Polytech. 

 Journal, LXXXV, 275.) We shall be .brief in this notice, as pro- 

 bably much that is contained in the article mentioned is well known. 

 In order to avoid the necessity of arranging before each charge the 

 fine iron wire between the conductors, Roberts invented cartridges, a 

 number of which can always be prepared in advance. They are made 

 in the following manner : two copper wires, each 10 feet long and 1 line 

 thick, well covered with waxed cotton or woolen yarn, are placed side 

 by side close together ; at one end they are twisted together for aborit 

 6 inches, as represented in Fig, 57, and their extremities left to form 

 a fork, a little over ^ inch long, with its extremities l, 

 inch apart ; the ends of this fork are then laid bare, 

 cleaned by filing, and the fine iron wire is stretched 

 between them. The iron wire is wound around the 

 extremities of the copper wires, and may then be soldered 

 with tin. 



The iron igniting wire is, of course, destroyed by each 



explosion ; to save the conducting copper wires they 



are firmly tied together with twine, as indicated in the 



!fio;ure, and then wound around with fine binding wire. 



I The body of the cartridge is a tin tube, 3 inches in 



[length and f to 1 inch in width, soldered and perfectly 



I water tight. (A glass tube might probably answer.) 



' The fine iron or steel wire is placed at aboat the middle of 



; the cylinder, and is kept in its place by means of a cork 



I which closes the cylinder, and through which the 



I twisted copper wires pass. It is best to cut this cork 



• lengthwise, and after putting the wire between the 



two halves, to press them into the tube. But on account 



of the thickness of the conducting wires it will probably 



be found more convenient to make a groove in the cork 



for their reception. The cork being put in so that the 



fork is nowhere in contact with the sides of the tube, it 



is covered with a good cement. Roberts recommends a 



mixture of one part beeswax and two parts rosin. 



The tube is then to be filled through its open end 

 with dry sporting powder, and closed by another cork, 

 which must also be covered with the cement. 



Figure 58 represents the entire cartridge. Figure 59 shows how 

 the cartridge is pla,ced in the hole; 



* Our author could not possibly have seen Dr. Hare's description of his apparatus when 

 he wrote this sentence. The original notice (Am. Jour. Science and Arts, vol. 21, p. 139, 

 1832,) shows that Dr. Hare's apparatus was not complex, and that it was essentially the 

 eame as that here desciibed as the contrivance of Roberts. Gr. C. S. 



27 s 



