Intelligence and Miscellaneous Articles. 257 



zero, although it takes up again at each period its initial positiou . 

 The work is not nil, because the forces producing it depend at each 

 instant on the velocity of the electrized body, and not merely on its 

 position. Therefore the magnetized needle furnishes a finite quan- 

 tity of work, which becomes infinite with the number of the periods. 

 Besides as the system travels along a closed cycle, this work is de- 

 rived entirely from the forces which maintain the motion of the 

 electrized body. That body is therefore itself submitted to resistant 

 forces, which depend on the velocity of the magnetized needle. It 

 is the existence of these last forces that we wish to demonstrate. 

 If Rowland's effect is the analogue and as it were the complement 

 of the phenomenon discovered by QErsted, the inverse phenomenon 

 here signalized corresponds in the same manner to induction. It 

 is even found that moving a magnetic field produces, upon a small 

 body charged with a unit of electricity, a mechanical force equal in 

 amount and direction to the electromotive force at the same place ; 

 only we have here not an electromotive force without action on the 

 masses, but a force properly so called. 



From the preceding a curious consequence may be deduced ; it 

 is, that static electricity possesses a proper mechanical inertia, 

 which is simply added to that of the electrized body. If, indeed, 

 an electrized body is in motion in a space where there is no mag- 

 net, this motion gives rise to a magnetic field, since a magnetic 

 needle in its vicinity would be deflected. The intensity of the 

 magnetic field is proportional to the velocity; and consequently 

 the variation of that intensity is proportional to the acceleration 

 of the body. Now, from what we have seen above, the variation 

 of a magnetic field produces upon an electrized point a mechanical 

 force equal to the electromotive force of induction, consequently 

 proportional to the velocity of the magnetic variation, and there- 

 fore to the acceleration of the body, and with the same direction as 

 the acceleration. But a mechanical force directed thus, and propor- 

 tional to the acceleration, constitutes what is called a, force of inertia. 



The ratio of the force to the acceleration is a constant quantity 

 for the same electric charge, but not simply proportional to the 

 quantity of electricity. — Comptes Rendus de VAcademie des /Sciences, 

 July 21, 1879, t, lxxxix. pp. 151-153. 



ON THE SENSIBILITY OF THE ORGAN OF HEARING. 

 BY W. KOHLRAUSCH. 



With the aid of a toothed wheel working against a disk of metal 

 or pasteboard, Savart * fouud that two impulses can make upon the 

 ear the impression of a comparable tone ; M. E. Exner t finds by 

 means of tuning-forks vibrating before spherical resonators that 17 

 impulses, M. Pfaundler t again, by experiments on holed sirens and 

 reflection-tones, that only two impulses are required ; lastly, M. 

 Auerbach§, nearly in accordance with M. Exner, that about 20 vibra- 



* Ann. de Chim. et PJn/*. xliv. p. 348 (1830). 



t Pfiiiger's Arch w,xm. p. 228 (187G). 



| Wien. Ber. lxxvi. p. 572 (1877); cf. A. Seebeck, Pogg. Ann. liii. 

 p. 417 (1841). § Wied. Ann. vi. p. 591 (1879). 



