NATURAL PHILOSOPHY. 159 



yond that required. The secondary wire is insulated from the 

 primary by means of an ebonite tube of one-half an inch in thick- 

 ness and 8 feet in length. 



"The length of the secondary coil is 54 inches, the diameter >s 

 19 inches, and without the internal ebonite tube containing the 

 primary wire and iron core it is a cylinder 19 inches in diameter 

 and 6 in(?hes thick. 



"The condenser, made in the usual manner with sheets of var- 

 nished paper and tinfoil, is arranged in 6 parts, each coiUaining 

 125 superficial feet, or 750 square feet of tinfoil in the whole. 



'* A large and substantially made contact breaker, detached 

 from the great coil and worked by an independent electro-mag- 

 net, was constructed, and worked very well with a comparatively 

 moderate power of 10 or 20 large Bunsen's cells, when, however, 

 the battery was increased to 30 or 40 cells, it became unmanage- 

 able. 



"A Foucault break, with the platinum amalgam and alcohol 

 above it, was now tried, and answered very much better than the 

 ordinary contact breaker ; there was no longer any burning or 

 destruction of the contact points, although the great power of the 

 instrument appeared to cause continued decomposition in the 

 water of the alcohol placed above the platinum amalgam,- and 

 every now and then the spirit was violently rejected, probably by 

 explosion of the mixed gases taking place in the amalgam, in 

 which they collected in bubbles ; the alcohol took fire constantly 

 and had to be extinguished. A large and very strong glass vessel 

 (in fact, an inverted glass cell belonging to a bichromate batter}') 

 was bored through, and the neck fitted into a cap with cement, a 

 thick wire covered with platinum being inserted in the bottom ; 

 the platinum amalgam was poured on this, and over it a pint or 

 more of alcohol ; the contact wire was also very thick and pointed 

 with a thick stud of platinum, and, being attached to a spring, 

 contact was easily made and broken. Explosions did not occur, 

 flashes of light could be seen between the amalgam and the 

 alcohol, and the height of the column of the latter prevented the 

 forcible ejection of the spirit, which no longer took fire. The 

 break was used for 8 hours in a continuous series of experiments. 



"The Bunsen's battery used in the experiments was made with 

 the largest porous cells that could be obtained, and each cell con- 

 tained about one pint of nitric acid. 



" Some experiments were tried with the battery arranged for 

 intensity, and used with the complete condenser of 750 square 

 feet of tinfoil, and 1,500 square feet of paper. At first, 5 cells 

 were used, and these gave a spark 12 inches in length. The 

 number of cells were gradually increased until 50 wore in opera- 

 tion, when a spark from 28 to 29 inches in length was ob- 

 tained. 



" In order to ascertain whether any variation in the size of the 

 condenser would affect the length of the spark, a number of ex- 

 periments were tried ; and it was found that when half the con- 

 denser was used the spark increased in length up to 20 cells, but 

 not after. 



