186 Mr Wilson, On a Portable Gold-leaf Electrometer, etc. 



strip of the silvering being, however, removed from each plate 

 to enable the gold leaf to be seen. The inner case screws on to 

 the top of a brass rod passing through the neck of the quartz 

 Leyden jar and connected with its inner coat. The jar is enclosed 

 in the hollow pedestal which supports the instrument. The top 

 of the pedestal, with the outer case of the electrometer which it 

 supports, can be screwed off; and into a tube about 1 cm. wide 

 projecting from the under side of this cover a tube cemented 

 round the base of the quartz tube slides stiffly. This admits of 

 the inner case of the electrometer being adjusted to be concentric 

 with the outer. 



The quartz bulb is rather less than 2 cms. in diameter, the 

 tube 4 or 5 mm. in external diameter. The bulb and tube 

 are silvered internally, contact being made between the inner 

 coat and the brass rod by means of a strip of tinfoil gummed 

 at the ends. The outer coat is of tinfoil. I have found such 

 Leyden jars, which have an electrical capacity of from 50 to 

 100 cms., extremely useful on account of their almost perfect 

 insulation. The bulbs were obtained from Messrs Baird and 

 Tatlock, and have been made with the blowpipe 



The gold leaf is about 1*1 cms. long and very narrow. . That 

 in use at the present time is about -^ of a mm. wide, but it is 

 fairly easy to cut leaves of this length -jL of a mm. or less in width. 

 The point of attachment of the leaf is a little to one side of the 

 centre of the inner case, being at the tip of a small projection on 

 the supporting wire. This wire is about 1 mm. in diameter, the 

 projection reaching a distance of about \ a mm. from its surface. 

 The wire passes through an aperture at the top of the inner case 

 about 5 mm. in diameter, then through a quartz tube, by means 

 of which it is insulated from the outer case ; it is attached to a 

 brass terminal closing the top of this tube. The quartz tube fits 

 into a short tube projecting from the bottom of the terminal, 

 so that a very small quantity of cement (sealing-wax) is necessary 

 to fix it tightly. It is also cemented about the middle of its 

 length within a hole through the flat end of a brass tube about 

 1 cm. wide and 1 cm. long. This slides stiffly in a short tube at 

 the top of the outer case of the electrometer. It is thus easy at 

 any time to remove or replace the gold leaf. 



For the purpose of charging the inner case and Leyden jar 

 a side tube is attached to the outer case ; into this is fixed a glass 

 tube with a platinum wire sealed through its outer end and pro- 

 jecting from its inner end to within a few mm. of the wall of the 

 inner case. The inner case is then charged simply by sparking in 

 from an electrophorus or electrified rod till the desired deflection 

 is obtained with the gold leaf earthed. To another side tube a 

 drying bottle may be attached. 



