65 



Mr. J. H. Pepper on so me Experiments [June 17, 



The total resistance of the primary is 2*201400 British Association units ; 

 and the resistances of the primary conductors are, respectively, for three 

 strands '733800 B.A.U., six -366945 B.A.U., twelve -1834/25 B.A.U. 



The primary core consists of extremely soft straight iron wires 5 feet in 

 length, and each wire is -0625 of an inch in diameter. The diameter of 

 the combined wires is 4 inches, and their weight is 123 lbs. 



The secondary wire is 150 miles in length ; it is covered with silk 

 throughout ; and the average diameter is -015 of an inch. 



The total weight of this wire is 606 lbs., and the resistance 33,560 B. A. 

 units. The insulation throughout is greater by 95 per cent, than the strain 

 upon the coil during its action. The secondary wire is insulated from the 

 primary by means of an ebonite tube J an inch in thickness and 8 feet in 

 length. 



The length of the secondary coil is 54 inches, the diameter is 19 inches, 

 and, without the internal ebonite tube containing the primary wire and iron 

 core, it is a hollow cylinder 19 inches in diameter and 6 inches thick. 



The condenser, made in the usual manner with sheets of varnished paper 

 and tinfoil, is arranged in six parts, each containing 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 electromagnet, 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 unmanageable. 



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 con- 

 tinued decomposition in the water of the alcohol placed above the platinum 

 amalgam, and the spirit was frequently ejected, 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 the inverted glass cell of a bichromate 

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

 thick wire covered with platinum being inserted in the cap ; the platinum 

 amalgam was poured on this, and over it a pint of alcohol ; the contact wire 

 was also very large, and pointed with a thick stud of platinum, and, being 

 attached to a spring, contact was easily made and broken. Flashes of light 

 could be seen between the amalgam and the alcohol ; but explosions did not 

 occur, and the height of the column of the latter prevented the forcible 

 ejection of the spirit, which no longer took fire. This break was used for 

 eight 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 contained about one pint 

 of nitric acid, the immersed carbon being 50 superficial inches in each cell. 



