462 F. Dellmann on the Observation of Atmospheric Electricity. 



fine glass thread reaches into this vessel, and carries a fine brass 

 wire, i (the arm of the balance), about 2 inches long, in a hori- 



zontal position, above a strip of thin brass plate of the same 

 length and about 1 line broad. The arm of the balance is ham- 

 mered out flat, so that its flat faces are vertical. The strip of brass, 

 the plane of which is also vertical, is fastened into a narrow slit 

 on a brass wire, A, about half a line in thickness, which passes insu- 

 lated through the bottom of the brass vessel and extends about 2 

 inches beyond. By means of this wire the electricity to be mea- 

 sured is imparted to the instrument, on which account I have 

 given it the name of the conducting wire [Zuleitungsdraht) . On 

 the bottom of the inside of the brass vessel, that is, beneath the 

 brass strip, a brass graduated circle, /', is also placed, which must 

 be sufficiently polished to form a mirror. If the upper index be 

 turned, the arm of the balance also turns. The stationary strip of 

 brass in the lower vessel is fixed at 0°. The instrument is adjusted 

 when the index above, and the arm of the balance below, point 

 to the same numbers on the two scales. When reading off the 

 angle below, the error of parallax is avoided by making the image 



