80 Intelligence and Miscellaneous Articles. 



ON THE MANNER IN WHICH THE CURRENT OF AN INDUCTION 

 FRICTIONAL MACHINE IS AFFECTED BY THE MOISTURE. BY 

 R. KRUGER. 



The results of this investigation may be summarized as follows : — 



1. The connexion between the strength of the current of an in- 

 duction machine and the moisture may be expressed by the formula 



i=i -ap 2 =i (l-£ T ); 

 \ Po / 



in which i is that strength of current which would be obtained if 

 there were no moisture at all, and p is that degree of moisture at 

 which the machine would not work. This formula holds for any 

 degree of relative moisture with perfect accuracy. 



2. The constant p =\ / la is greater as the velocity of rotation 



V a 

 increases ; that is, when the machine is rotated with greater velocity, 

 its current first disappears at higher degrees of moisture than when 

 the rotation is less rapid. 



3. The quantity of electricity given by one turn of the plate 

 when there is no moisture is essentially independent of the velocity 

 of rotation; and the quantity of electricity which in this case 

 passes through the section of the conducting wire amounts to 

 458,33 . 80 5 electrostatic units. 



Some observations intended to ascertain how far the current 

 depends on the distance of the points from the movable plate, and, 

 on the other hand, on the distance of the plates from each other, 

 showed a decrease of strength with greater distance ; but it was 

 not possible to establish a definite law. — "Wiedemann's Anncden, 

 No. 6, 1884. 



BOYLE'S LAW. A LECTURE EXPERIMENT. 

 BY J. L. ANDREAE. 



In a glass tube, about a metre long and from 1| to 2millim. in- 

 ternal diameter, closed at one end and open below, is introduced 

 a thread of mercury about 250 millirn. in length. This encloses a 

 certain volume of air, which is about 40 cub. centim. 



The tube is supported on a stand, which has a scale on white 

 paper divided in centimetres, and can be placed on the table with 

 either end vertical. If H is the height of the barometer in milli- 

 metres, the pressure of the enclosed air is P = H— 250. If the 

 tube is inverted, the pressure is P'=H + 250. If 11=750, P=500 

 and P' = 1000, so that the volume is reduced from 40 to 20. 



This simple apparatus has the advantage that it is always ready 

 for use, and hence does not need to have the mercury poured in 

 as in the usual form. — Wiedemann's Anncden, No. 6, 1884. 



