OF ARTS AND SCIENCES. 451 



its broadest parts about 2 era. in width. The supporting platinum 

 rod terminates in a small half-loop, just below the quadrants. To 

 this loop a very fine platinum wire is attached, supporting a light lead 

 paddle in the sulphuric acid of the glass jar. The quadrants are made 

 of polished brass, the circle of which they are sections having a diame- 

 ter of 15 cm. They are mounted on glass tubes, made of the best 

 white glass, 5 cm. in height, and 1 cm. in diameter, and mounted on 

 gutta-percha. Through the inside of the tubes run insulated wires 

 imbedded in rubber, connected at the upper end with the quadrants, 

 and at the lower end passing through the brass base plate to binding- 

 screws in the walls of the lower compartment. 



One of the quadrants can be slid out, the supporting rod being 

 inserted in a brass plate moving in a groove cut in the base plate. 

 A spring plate with a small projecting knob, fitting into the notches 

 of the base plate, keeps this quadrant perpendicular and firm wher- 

 ever it may be placed. 



The lower compartment is 23 cm. high and 20 cm. square. In it 

 is placed a glass jar of 15 cm. diameter and 10 cm. depth. The 

 vessel is tinfoiled on the outside and bottom, and rests on a circular 

 brass plate which can be either elevated or lowered several inches. 

 The back of the compartment is hinged, and when opened allows full 

 inspection. A platinum wire imbedded in gutta-percha passes through 

 the side of the glass vessel about a centimeter from its upper edge. 

 'J his wire dips into the acid of the jar. 



The instrument, thus constructed, has been in constant use during 

 the past six months, and, requiring but little attention, has proved 

 itself very well adapted for work of this nature. 



Multiple Quadrant Electrometer. 



With a view to the construction of a portable electrometer suffi- 

 ciently sensitive and accurate, the following instrument was designed 

 by Professor Trowbridge and Mr. McAdie, and built according to 

 their plans by the "Western Electric Company of Boston. An exterior 

 wooden case 30 cm. high and 12 cm. square, contains four compounded 

 quadrants, a compound needle, and the suspending and charging ar- 

 rangements. The outer case rests on a brass plate with the proper 

 levelling arrangements, and is divided into three compartments, let- 

 tered A, B, and C. Each of these has one side at least hinged, so as 

 to open and allow easy access to the interior. At the bottom of the 

 front side of compartment A, a .semicircular glass case 2 cm. in height 

 projects. The bottom inside surface of this is mirrored in order to 



