388 



RECENT PROGRESS IN PHYSICS. 



Instead of expressing the connexion between the quantity of elec- 

 tricity with which the electrometer is charged, and the divergence of 

 the pendulum, by means of a complicated formula, I hpve attempted 

 to render it apparent by graphic representation. In fig. 30, the ordi- 

 nates represent the quantities of electricity, the abscissas the diver- 

 gences, and the marked points are those which correspond to the mean 

 divergences belonging to the different quantities of electricity marked 

 on the sides of the figure. 



These points admit of being connected by a quite regular curve, as 

 shown in the figure^ representing the relation between the quantity 

 of electricity and the divergence, the points corresj)onding to 6 and 7 

 only lying a little outside of the curve. 



The readings, from which these results were taken, were indeed 

 exact only to a half degree; a greater nicety in reading the single 

 observations is not necessary, since the results (from various causes) 

 are uncertain beyond one half degree, and the separate readings for 

 the same quantity of electricity often differed as much as two degrees. 

 Knochenhauer, indeed, gives single minutes in his observations, 

 although the uncertainty of the observation amounts to several de- 

 grees ; how he could read to single minutes with an instrument so 

 small as his, (44,) it is difficult to conceive ; if, however, the instru- 

 ment actually admitted of so accurate a reading, it was still unneces- 

 sary, because the pointing of the needle is not determinable with the 

 same degree of accuracy. In such cases greater accuracy should not 

 be affected than is actually to be obtained under the circumstances. 



After the straw electrometer had been tested in the above described 

 manner, I proceeded to the different experiments, which were ar- 

 ranged in the following manner : 



A hollow brass ball, two inches in diameter, was suspended by a 

 well insulating silk string. Directly under it stood the electrometer, 

 upon a plate whose support could be slipped up or down and fastened 

 at any desired position. The brass plate of the electrometer was 18 

 lines in diameter. 



On the rod which bore the plate of the stand three 

 marks were made, at distances of 3 inches from each 

 other. When the lowest of these marks was at the 

 upper end of the hollow leg, the plate of the elec- 

 trometer was 3 inches from the middle point of the 

 ball ; and this distance amounted to G and 9 inches 

 when the second and third of the marks were simi- 

 larly placed. Three inches being taken for unity, 

 the electrometer plate could be shifted to the re- 

 spective distances, 1, 2, and 3. 



When the plate of the electrometer stood at the 

 -'istance 3 from the ball, it was touched with the 

 finger, and the ball a charged by bringing a small 

 Leyden jar into contact with it. 



As soon as the ball was charged in this manner, 

 the jar was quickly put aside. 



The electricity on a had then rendered latent a 

 definite quantity of the opposite E on h, which 



Fiff. 31. 



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