Intelligence and Miscellaneous Articles. 259 



directly, by rneans of a spring dynamometer, the work required for 

 the induction of an electric current of determined strength in a 

 circuit of given resistance, and comparing it with that calculated 

 from theory. 



A magnetoelectrical machine for continuous currents served for 

 the induction-apparatus, the electromotive force of which had 

 previously been exactly ascertained and found to be proportional 

 to the number of turns. The dynamometer was a dynamometric 

 winch of the newest construction, provided with a rnarking- 

 apparatus for sketching the work-curves. Its scale was tested by 

 direct loading, and found accurate. The dynainoinetric winch was 

 screwed to the induction apparatus on an axle attached to the 

 machinery instead of the ordinary winch. 



For the measurement of the induced currents a tangent 1 compass, 

 the reduction-factor of which was exactly ascertained, was inserted 

 in the circuit, of which the resistance was measured as accurately 

 as possible, and could be altered at pleasure by means of inserted 

 scales. For counting the number of turns a seconds' pendulum 

 with a loud stroke was used. 



Five experiments were made : in three the velocity of rotation 

 amounted to 1 revolution of the winch in 1 second (corresponding 

 to 7 revolutions of the inductor) ; in the two other experiments 1 

 turn of the winch took 2 and 4 seconds respectively. In each 

 experiment 65 turns were executed — once wdth interrupted, and 

 once with closed circuit. The difference between the work recorded 

 by the dynamometer in the one case and in the other was the 

 work of induction expended for the production of the current 

 simultaneously measured on the tangent-compass according to the 

 proportion of the electromotive force calculated from the number 

 of turns or from the known resistance. It amounted, according 

 to the very well accordant results of the five experiments, in which 

 the expenditure of induction-work lay between the limits of 1 and 

 6 meter-kilograms, to the electromotive force of one Daniell element, 

 and to the resistance of one Siemens unit, reduced 0*13 metre- 

 kilogram per second — a result which comes very near theoretical 

 determinations. 



Comparing this value of the work with the number of calories 

 corresponding to the chemical processes that take place in a Daniell 

 series with equal resistance, we get for the mechanical equivalent 

 of the heat, on using the numbers given by "W. Thomson and 

 Jenkin, the number 428, or, if we take as the basis of the cal- 

 culation the higher amount of induction-work in the first four ex- 

 periments, the number 421, very closely agreeing with the generally 

 accepted equivalent of Joule. — Kaiserliche AJcademie der Wissen- 

 scJiaften in Wien, mathematisch-naturwissenschaftliche Classe, July 3, 

 1879. 



ON THE RADIOMETER. BY DR. J. PULUJ. 

 The paper contains a criticism of the evaporation theory of 

 Osborne Reynolds and the emission theory of Zollner, 



