258 BEXT.T. PIKES, JR., DESCRIPTIVE CATALOGUE. 



Fig. 273. 



rod. On one side is a row of sharp points, to draw the 

 electricity from the glass ; and on the other, a hole, having 

 a wire with a brass ball thereon. A flap of black silk, or 

 oiled silk, is attached to the rubber, to prevent the dissipa- 

 tion of the electricity from the surface of the cylinder before 

 it reaches the points. Price, 4-inch, $8.00. 



" 5-inch, $10.00. 



" 6-inch, $12.00. 



The Electrophorus. (Fig. 274, next page.) The electro- 

 phorus is certainly a very remarkable source of electrical 

 accumulation, and is an instrument which, for many light 

 experiments, forms a good substitute for the electrical 

 machine. It consists of a metallic plate, with a rim about 

 half an inch deep, containing a resinous plate, formed of 

 equal parts of shellac, rosin,. and Venice turpentine melted 

 together, and about ten to fourteen inches in diameter, and 

 half an inch thick, on which rests a brass or metal plate, 

 from eight to twelve inches in diameter, having well-rounded 

 edges, and a glass handle at the centre about ten inches 

 long, for the purpose of lifting without drawing off the 

 electricity ; a wire with a brass knob is usually connected 

 with the plate for taking the sparks ; a, a, a, represent 

 brass rods connected with the lower plate having their tops 

 level with the plate of resin, by which is avoided the trouble 



