F. Dellmann on the Observation of Atmospheric Electricity. 461 



rod is fastened, which reaches so far upwards that a crosspiece 

 fastened to it and directed towards the carrier of the collector, 

 touches the carrier immediately above the case, when the shorter 

 arm of the lever is depressed. The shorter arm of the ruler is 

 bored through at its extremity, and a thin brass we passes 

 through the hole and is carried downwards. The brass wire 

 carries a brass handle at its lower extremity for the convenience 

 of taking hold of it, and is so long that when the sphere is raised , 

 above the roof of the house, the handle reaches to the mndow 

 from which the sphere was placed upon the pole. On pulhng 

 the handle, the crosspiece mentioned strikes upon the carrier of 

 the sphere, whereby the latter becomes charged. On letting go 

 the handle, the angular lever falls back, because it is heavier on 

 the side on which the crosspiece is situated. The sphere is then 

 lowered, removed from the pole, and the electricity which it has 

 brought with it given, by means of a transferrer, to the measurer. 

 As the sphere acquires its electricity in the way described, it 

 must always bring down the opposite electricity to that of the 

 atmosphere. A measurement is completed in a few seconds. 

 By placing the sphere, during the interval between two measure- 

 ments, upon a tripod in a room, it may be retained for a long 

 time in an insulated state ; and inasmuch as it can easily be taken 

 with its carrier out of the case in which it stood upon the pole, 

 any possible want of insulation may be checked and corrected. 

 The sphere, while being charged, is remote from the observer, so 

 that his presence cannot exert any such influence as must have 

 been the case with the observations made at Brussels and Munich. 

 When the sphere is elevated, the whole apparatus is fixed in its 

 position by means of a windlass and break, which are placed by 

 the drum upon which the cord is wound. In this condition 

 the apparatus is a stationary one, but it may be converted into 

 a moveable one by lowering the break. 



The torsion of a glass thread is employed to measure the electri- 

 city, for there is no force so constant and reliable for this purpose 

 as the elasticity of glass. The glass thread m (see woodcut) is stuck 

 with shell-lac upon the end of a brass rod, t, about 2 hnes in thick- 

 ness, so as to be in the same straight line with the axis of the 

 rod. Fastened to the rod with a screw, there is an index, u, which 

 moves above a graduated circle, a'. The brass cylinder supporting 

 the plate on which is the graduated circle, is firmly pressed upon 

 a glass tube, s, of tolerable thickness, which is provided with an 

 external ring of leather for this purpose. The lower end of the 

 glass tube is also furnished with a leather collar, by which it is 

 firmly fastened into a second brass cylinder, o, which passes through 

 a tliick piece of plate glass, n. This glass plate forms the cover to 

 a jar- shaped vessel of thick brass. The lower end of the very 



