[ 392 ] 

 XLIX. Intelligence arid Miscellaneous Articles. 



CALORIFIC EFFECTS OF THE MAGNETISM IN AN ELECTROMAGNET 

 "WITH SEVERAL POLES. BY A. CAZIN. 



T HAVE observed the calorific effects which accompany the disap- 

 pearance of magnetism in the core of a rectilinear electromagnet 

 presenting several consequent points, and have arrived at a very- 

 simple law : — 



When a rectilinear core of iron is magnetized by a series of identical 

 coils through which the current passes in alternately opposite directions, 

 if the coils determine equal concamerations, the quantities of heat pro- 

 duced in the core by the disappearance of magnetism are inversely 

 proportioned to the squares of the numbers of concamerations. 



The apparatus I used is a sort of differential air-thermometer, 

 the reservoirs of which are formed by iron cylinders 42 centims. in 

 length, 5 centims. in diameter, and about 2 millims. in thickness. 

 The bases of these cylinders are closed by plates of copper. A 

 glass tube haviug an internal diameter of 2 millims., bent in the 

 shape of a U and containing water, unites the two cylinders : it 

 serves as a manometer to measure the difference of pressure, H, 

 which establishes itself between the two reservoirs when one of 

 them is heated ; and if it is only a question of relative thermic 

 effects, we may content ourselves with observing this difference of 

 pressure ; it is proportional to the difference of temperature of the 

 two reservoirs. 



In order that these reservoirs may be in the same conditions in 

 regard to their surroundings, each of them is enveloped in a coating 

 of cotton and a tube of pasteboard ; and then two are placed in the 

 axis of two identical bobbins of wood without contact between the 

 wood and the pasteboard. The copper wire which receives the cur- 

 rent is coiled round one of the series of bobbins, and can magnetize 

 the corresponding core. These precautions are necessary in order 

 that the voltaic heat of the wire may not be transmitted to the core. 

 I ascertained that this condition was satisfied : the current remain- 

 ing closed for a long time, the water manometer indicated only an 

 insignificant change. 



To make an experiment, a discontinuous current is thrown into 

 the magnetizing coils ; a tell-tale registers the number n of the in- 

 terruptions ; at each minute the difference of the levels in the ma- 

 nometer is noted ; and the noting is continued when the current is 

 suppressed, until the initial levels are restored. A graphic sketch 

 of these data makes known, on the one hand, the total effect H. pro- 

 duced during the action of the discontinuous current, and, on the 

 other, the correction h due to the cooling action of the surrounding 

 bodies. Dividing H + h by the number n of the interruptions, we 

 have the effect of the disappearance of magnetism at each breaking of 

 the voltaic circuit. This quantity serves as a relative measure for 

 the hea^b generated by the magnetism. 



