252 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



together by a stout brass spring, having a screw to give 

 them the required pressure ; supported on a stout swelled 

 glass pillar, cemented into a polished brass base, and being 

 tirmly held by a screw and nut beneath the frame. Over 

 the rubber is mounted a large and well-polished brass ball, 

 which is the negative conductor. The positive conductor is 

 a well polished brass cylinder, having swelled ends ; the one 

 having arms embracing the plate with rows of points for col- 

 lecting the fluid ; the other having a wire with a ball. The 

 conductor is supported on a stout swelled glass pillar, 

 mounted in a socket, by which the pillar can be separated 

 from the conductor, and at the frame cemented in a base, as 

 the rubber, with nut and screw to fasten. The frames are 

 made of mahogany or rosewood, highly polished, and the 

 brass work elegantly finished. The plate and all the pillars 

 are attached by nut and screw, and may be taken off for 

 convenient transportation. 



Price, 16-inch, $20.00 and $25.00. 



20-inch, $34.00 and $38.00. 



24-inch, $50.00. 



30-inch, $85.00. 



36-inch, $130.00. 



42-inch, $200.00. 



Nairne's Cylinder Electrical Machine (Fig. 271, next page) 

 consists of a hollow cylinder of glass, usually eight to ten 

 inches in diameter, supported on a rectangular base, as in 

 the preceding machines described. Two hollow metallic 

 conductors, about twenty inches in length and four inches 

 in diameter, having hemispherical ends, are placed parallel 

 to the cylinder, one on each side, upon two insulating pillars 

 of glass, which are cemented into two separate pieces of 

 wood, that slide across the base so as to allow of their being 

 brought within different distances of the cylinder, and having 

 screws entering the base for clamping fast. To one of these 

 conductors the cushion is attached, being fastened to it by 

 a spring and two brass rods fastened to the cushion, the 

 rods entering holes for the purpose in the conductor, and 

 moving freely therein ; the spring causing it to press equally 

 against the cylinder in every part of its revolution. The 

 pressure of the cushion is also further regulated by the 

 adjusting screw at the base. From the upper edge of the 

 cushion there proceeds a flap of black silk, which is 



