INDUSTRIAL PEOGUESS DURING THE YEAR 1876. xlv 



PHYSICS. 



By GEORGE F. BAKKER, 

 Professor of Physics in the University of Pennsylvania, Philadelphia. 



The progress in physical science has been fully up to that of pre- 

 vious years. In General Physics^ Crova has suggested a most excel- 

 lent experiment for showing the relation of heat, electricity, and 

 mechanical work to each other. The apparatus used is a Clamond 

 thermo-battery, a Gramme magneto-electric machine, and a coil of 

 platinum wire inclosed in a glass globe. First, if the wire coil be 

 attached to the battery alone, the heat from the gas flame, trans- 

 formed into electricity by the battery, reappears as heat in the ex- 

 ternal circuit. Second, if the Gramme machine be '^wt in the circuit 

 in place of the coil, the electricity developed by the heat is trans- 

 formed into mechanical w^ork, and the machine acts as a motor. 

 Third, if both coil and machine are put in circuit, heat is produced 

 in the coil, and work in the machine. But if now the machine be 

 stopped, the incandescence of the wire is increased ; as it gradually 

 acquires velocity again, the glow of the wire is reduced. The ex- 

 penditure of heat necessary to produce a given quantity of work is 

 thus made evident to the eye. Finally, if the machine be turned by 

 hand in the direction of its previous rotation, the incandescence of 

 the wire diminishes, until finally a A^elocity is reached at which the 

 wire no longer glow^s at all. But if the rotation be in the opposite 

 direction, the incandescence increases until the wire fuses. The ad- 

 ditional energy introduced appears as heat. 



Ettingshausen has made an ingenious use of the stroboscoj)ic 

 method of Mach for the purpose of studying the uniformity of mo- 

 tion of rotating bodies. The rotations compared were obtained 

 with an electro-magnetic motor w^ith Helmholtz's regulator and an 

 accurately constructed clock-w'ork. The former of these gave the 

 most uniform motion. 



Another noteworthy event has been the presentation to the Royal 

 Society of a paper by C. W. Siemens, describing an instrument to 

 which he gives the name of bathometer, and by wdiich the depth of 

 water at any point in the ocean may be ascertained by simple in- 

 spection, without the use of a sounding-line. It consists of a vertical 

 column of mercury inclosed in a steel tube having cup-like exten- 

 sions at its ends. The lower end is closed by a corrugated steel 

 diaphragm, the weight of mercury resting upon it wdiich is of 

 course affected by the force of gravitation being balanced in the 



