398 MEMORIAL OF JOSEPH HENRY. 



length is less, the minute motions diminish too slowly; if greater, 

 their intensity is too much enfeebled." * 



Note G. (From p. 

 WHEATSTONE'S CHRONOSCOPE. 



For the purpose of measuring and registering extremely short 

 intervals of time, Professor Charles Wheatstone, extending his earlier 

 experiments of 1834, on the velocity of electricity by means of a 

 revolving mirror, projected a " chronoscope " based on the automatic 

 agency of electro-magnetism. Among the applications in view 

 were the determination of the exact times of falling bodies, the 

 duration of an explosion of gunpowder, etc. At what time this 

 ingenious device was practically developed, it is difficult to say; 

 but we learn that M. Konstantinoff, an accomplished Russian Artil- 

 lery Officer, visiting England in 1842, had this project shown or 

 explained to him by Professor Wheatstone. Looking at the possi- 

 bilities of this suggestion from his professional stand-point, M. 

 Konstantinoff at once directed his attention to the contrivance of a 

 modification of the arrangement, adapted to measure the velocity 

 of a projectile at various points of its flight. Invoking the well- 

 known electrical knowledge and skill of his friend Mons. L. Bre- 

 guet of Paris in 1843, the two commenced in June of that year the 

 construction of a machine which should indicate and record 30 or 

 40 successive observations within the few seconds of a projectile's 

 flight. The apparatus was successfully completed May 29, 1844; 

 and an account of it was read before the French Academy, January 

 20th, 1 845. f In this instrument, the various records were made on 

 a timed revolving cylinder, by styles or pencils, actuated by electro- 

 magnetic motions at the several moments of breaking successive 

 circuits. Wheatstone's reclamation, and account of his own inven- 

 tion, were published four months later, through the same channel. { 



The two chronoscopes were undoubtedly the same in principle, 

 although Wheatstone's gave but two records; an initial one by 

 the falling or projected ball breaking the galvanic circuit, and a 

 terminal one by a re-establishment of the circuit on the ball striking 

 a horizontal or a vertical spring plate and thus causing a metallic 

 contact to be made. For measuring the interval, Wheatstone em- 



* Annales de Chimie et de Physique, 1827, vol. xxxiv. pp. 54, 55. 



t Oomptes Rendus, Jan. 1845, vol. xx. pp. 157-162. 



t Oomptes Rendus, May 26, 1845, vol. xx. pp. 1554-1561. 



