491 



The Construction of a Rutherford's Electroscope. 



Edwin Morrison. 



Introduction. 



At the suggestion of Dr. R. A. Millikan the author recently undertook 

 the problem of constructing an electroscope for general laboratory work in 

 radio-active measurements. The general outlines and plans suggested 

 by Dr. Rutherford in his original papers published in the Philosophical 

 Magazine and in his work entitled Radio-active Transformations have 

 been followed. Suggestions have also been taken from the following works : 

 Studies in Radio-activity, by Bragg ; Conduction of Electricity Through 

 Gases and Radio-activity, by McClung ; and Practical Measurements in 

 Radio-activity, by Makower and Geiger. 



The purposes have been, first, to show, in greater details than the 

 original papers give, the methods ot constructing a successful electroscope ; 

 and, second, to embody in one instrument as wide a range of experimental 

 work as possible. 



CONSTRUCTION. 



A diagram of the electroscope is shown in Fig. 1. The dimensions of 

 the gold leaf chamber (E) are Id x 10x10 cm. This chamber is con- 

 structed from sheet brass 1.7 mm. in thickness. The four plates for the 

 sides, top and bottom are first carefully jointed by means of a file and 

 tben soldered together as shown in Fig. 2 (A). To facilitate the process 

 of soldering two right angle pieces of metal are joined together forming 

 a right angle frame as shown in Fig. 2 (B). When two pieces of the box 

 are to be joined together they are carefully adjusted upon the frame, a 

 few small pieces of solder and soldering fluid are placed along the joint 

 and a pointed flame is directed along the joint in the inside angle until 

 the solder is thoroughly fused. In this way the parts of the electroscope 

 box can be joined together square and straight. 



The front side of the electroscope box is a hinged door. This door has 

 a window in it 6.5 cm. square covered with mica. Through this window 

 the gold leaf may be observed by means of a reading microscope. A dia- 



