ELECTRICAL MEASUREMENT. 449 



the stand that was on the top of it, is shown. The 

 next that followed was this one (Fig. 55). I got down 

 the weight to about one-half, and I was perfectly 

 satisfied then, and this one has gone up Goatfell 

 a great many times ; but it is fully described in 

 my book, 1 and in the Report I have referred to. 

 I was showing it with great pride on one occasion 

 to Professor Tait, and I said to him : " You should 

 get one like that." He said, " I will wait until you 

 can get one that you can put into your pocket. 

 Get one the size of an orange, and then I will have 

 it." That literally was the origin of this latest 

 portable electrometer. I felt rather challenged by 

 what he said, and in the course of my next run up 

 to Glasgow, Mr. White, who is so indefatigable in 

 making new things, and who has so admirable an 

 inventive capacity, helped me in my endeavour, 

 and we had something like this one. In the course 

 of a month, this very electrometer (Fig. 56) was got 

 into action. This is the first attracted disc electro- 

 meter. It differs from the portable electrometer 



1 Papers on Electrostatics and Magnetism ; Macmillan, London, 

 1884. 



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