238 Intelligence and Miscellaneous Articles. 



Poisson, to which we are led, admitting alone Mariotte's and Gay- 

 Lussac's law and the equivalence of sensible heat, which disap- 

 peared in the expansion, to the external work. But assuming that 

 heat is consumed not merely by external work but by a certain in- 

 ternal work, we arrive at a theoretical solution agreeing very well 

 with observed facts. It is sufficient to add to the equation express- 

 ing the equivalence^between the heat which disappeared and the work 

 produced, another equation which replaces Mariotte's and Gay- 

 Lussac's law, and of which this is only a particular case. The 

 general formula applicable to all bodies may be rationally demon- 

 strated from the principles of thermodynamics (G. A. Hirn, Exposi- 

 tion analytique et experiment ale de la Theorie Mecanique de la Chaleur, 

 2nd edit. p. 207). Not merely do our experiments prove the 

 existence of internal work in the expansion of vapour, but they also 

 confirm one of the consequences of the new theory, and give a 

 means of measuring internal work. — Comptes Bendus,Dec. 31, 1866. 



INDUCTION-CURRENTS ON TWISTING IRON WIRES THROUGH 

 WHICH A GALVANIC CURRENT IS PASSED. BY G.WIEDEMANN. 



The twistings of the molecular magnets in magnetic bars effected 

 by torsion may give rise to induction-currents which traverse the 

 bars in the direction of their axis, or circulate in a spiral in the axis 

 of which the bar is fastened. Both these phenomena have been used 

 by Wertheim and by Matteucci to determine the changes in the 

 temporary and permanent magnetic moment of iron and steel bars in 

 torsion — which may, however, be more accurately and completely 

 effected by direct measurement of the magnetism of the bars by the 

 deflection of a steel mirror suspended in front of them. 



In the same manner induction-currents are formed if an iron wire 

 is twisted through which a galvanic current is either passing or has 

 been passed. As a supplement to my earlier experiments on similar 

 matters, I beg to communicate a few experiments made in this 

 direction. 



1. Between a brass clamp fastened on a board, and a second clamp 

 provided with a divided circle, which could turn in a bearing screwed 

 on the table, a well-annealed iron wire of 1*3 millim. diameter and 

 400 millims. in length was stretched. The wire was surrounded by 

 a spiral of copper wire, the ends of which were connected with the 

 multiplier of a reflecting galvanometer at a distance of 3 millims. from 

 the torsion-apparatus. A galvanic current was next passed through 

 the iron wire, which was twisted by turning tbe rotating clamp. 

 The deflection of the mirror of the galvanometer indicated in this 

 the formation of an induction-current. After its occurrence, the 

 mirror recurred to its former position of rest, proving that the de- 

 flection could not have been directly produced by the magnetization 

 of the twisted iron wire. 



If the current passed through the iron wire traverses it from the 

 rotating to the fixed clamp (*• from back to front"), the current pro- 



