RECENT PROGRESS IN PHYSICS. 



came measurable by removing the finger from 6, and, at the same time, 

 pushing aside a with the hand. — A divergence of 6° was indicated. 



The plate of the stand was then raised 3 inches higher, so that the 

 distance between h and the centre of a was equal to 2, or (> inches, 

 and the experiment repeated, in the same manner, by applying the 

 same jar with its charge. — A divergence of 12° Avas now indicated. 



The same experiment, repeated for the distance 1, gave the diverg- 

 ence, 30°. 5. 



The electrometer was then placed at the position 2, 3, 2, 1, 2, 3, 

 &c., in succession, and the same experiment made. The result of the 

 observations are collected in the following table : 



With equal charges of the ball a the mean divergence 30°. 6 was 

 obtained at the distance 1; the divergence 11°. 4, at the distance 2; 

 and the divergence 6°. 2, at the distance 3. 



Equal charges of the ball a were obtained by bringing it in con- 

 tact with the knob of a Leyden jar charged once for all for the whole 

 series of experiments. The charge of the jar was, indeed, somewhat 

 diminished at each contact with the ball, but this diminution was 

 not sensible after the twentieth contact, as the above table shows. 



We shall now see how great the changes are which give to our elec- 

 trometer, the deflections, 30°. 6, 11°. 4, and 6°. 2. 



From a consideration of Fig. 30, it follows that the divergence, 

 30.6 corresponds to the electrical quantity 8 the divergence 11.4 

 to the quantity 2.25 ; and 6.2 to 0.95. The quantity of electricity 

 which the ball a renders latent on 5, is, therefore 



At the distance 1, equal to 8.00. 

 <' " 2 " 2.25. 



" '' 3 " 0.95. 



These numbers are very nearly in the ratio of 1 : 4 : 9 ; or in- 

 versely as the square of the distance. At the distance of 1, the read- 

 ing of the divergence is rather too small, which can be easily explained. 

 For such heavy changes of the electrometer, causing a deflection of 

 upwards of 30 degrees, the pendulum sinks more suddenly by reason 

 of the more rapid loss; thus, when the reading is taken, the original 

 divergence has already slightly diminished. 



A similar series in which the alternation was only between the single 

 and double distance, (4 inches being the unity of distance,) gave the 

 following result : 



