i8 7 i.] 



Electricity. 



559 



and its insulation, and has additional insulation of paraffin paper interposed 

 at regular intervals. 



The insulation between the primary and secondary consists of glass bells 

 and vulcanite spools so proportioned as to offer the greatest resistance at 

 points of highest tension, and proved by actual experiment to be 50 per cent 

 greater than a spark of 21 inches would penetrate under the existing conditions. 

 The condenser contains 325 square feet of tin foil insulated with oil silk, 100 

 square feet being in permanent connection with the primary circuit, and three 

 buttons throwing on 100, 75, and 50 feet respectively at will. The break-piece 

 is of the combined automatic and hand movement, attached by Mr. Ritchie to 

 all his large instruments, the automatic break being operated by a single cell 

 battery, connected or thrown out at pleasure by a button on the surface of the 

 condenser-case. The total height to upper surface of horizontal strip is 

 i8£ inches ; total length of base from end to end of round caps over primary, 

 40 inches ; height of base, 5 inches; width of base, 13 inches ; length of each 

 section of secondary bobbin, 13 inches ; external diameter of secondary bobbins, 

 g inches. 



The battery for exciting this coil was made according to Professor Morton's 

 direction, by Messrs. Chester Brothers, of New York, and consists of three 

 glass jars, 10 inches in diameter and 12 inches high, into which are lowered 

 by means of a windlass plates of carbon and zinc, 8 x 10 inches, five of each 

 occupying each jar. The liquid employed is the mixture of potassic bichromate 

 solution and sulphuric acid, now used in several forms of battery. When the 

 solution is fresh, an immersion of 3 inches develops the full power of the coil. 



In connection with a Leyden jar of i| square feet surface it produces sparks 

 of 2J inches in length, and with one of Professor Morton's secondary condensers 



Fig. 23. 



Fig. 22. 



(see "Journal Franklin Institute," vol. liii., p. 256) shown in the accompanying 

 cut (Fig. 22), and containing 20 coated panes, it gives sparks 14 inches in length, 

 and of the intense whiteness and loud report of the Leyden jar discharge. 



Blocks of glass 3 inches thick are penetrated, and seem to represent pretty 

 accurately the same resistance as the 21 inches of air, for when the points are 

 separated 21 inches, and other wires connected with the columns for piercing 

 the glass, several sparks will pass in air before one with a red flash goes 



