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' LVII. On the Obsei'vation of Atmospheric Electricity. 

 By F. Dellmann*. 



PROFESSOR W. THOMSON has had the goodness to 

 notice my method for the observation of atmospheric elec- 

 tricity; at his desire I have rewritten the following for this 

 periodical. 



The apparatus, consisting of the collector and the measurer, 

 has received a new construction at my hands, for the special 

 purpose of attaining the greatest possible accuracy of result. 



The essay by Duprez, which obtained the prize awarded by 

 the Brussels Academy in 1844, convinced me completely that 

 the collector must be moveable ; because a fixed one cannot be 

 relied upon for sufficient insulation, and because its insulation can 

 never be properly checked. The moveable apparatus which I 

 have constructed may at any time be used as a fixed one, and 

 can be immediately rendered moveable again. By its means I 

 have been enabled to show that the fixed apparatuses are subject 

 to two hitherto neglected sources of error; viz. first, that they 

 become charged too slowly, inasmuch as they require at least 

 from 20 to 25 minutes before they are completely charged ; 

 secondly, that the action of the atmospheric electricity upon the 

 collectors is never pure, but accompanied by the action upon the 

 part of the apparatus connecting the collector with the measurer. 



My collector has the following form : — A brass sphere, of 

 about 5 inches in diameter, is screwed upon a brass wire of abovit 



2 Hues in thickness and 15 inches in length. The lower end of 

 this brass wire, carrying the sphere, is fastened into a foot of 

 shell-lac of about 9 lines in thickness, and is provided, at a 

 height of about 4 inches, with an enveloping ring of shell-lac of 

 the same thickness. The collector can thus be placed in an insu- 

 lated slate in a cylindrical brass case, into the middle of which a 

 bottom is soldered. In this way the case may be placed with its 

 lower half enveloping the top of a pole of pine wood, which may 

 be raised or lowered by means of a cord passing over a couple 

 of pulleys. The pole passes through two iron rings fastened to 

 two iron arms, about 4 feet apart, fixed into the wall of the 

 house. The top of the pole is cased with iron for a length of 

 about 9 inches. A vertical slit, of about 2 inches in length and 



3 lines wide, is cut through the top of the pole and its iron 

 casing, immediately beneath the place to which the lower enve- 

 loping half of the brass case reaches. A brass ruler passes 

 through the slit, and may be turned like a lever in a vertical 

 plane about an iron peg which passes horizontally through it. 

 On to the one, and somewhat longer, arm of this lever a brass 



* Communicated by Prof. W. Thomson. 



