Intelligence and Miscellaneous Articles. 409 



position of the axis. The angle V is found by measuring b on the 

 divided circle. Twelve observations, by this method, made at the 

 end of the year 1881 and at the beginning of 1882 by three dis- 

 tinct observers, gave the result 



Induction-compass — dip-needle (Dover) = — f 50" + 9". 

 The result is thus almost the same, and it will be found that the 

 accuracy of the method leaves nothing to be desired. 



Moreover a complete determination requires less time than with 

 a dip-needle. The researches will still be prosecuted with modified 

 apparatus, and particularly with smaller ones. — Comptes Hendus, 

 January 14, 1884. 



ON THE HEATING OF IRON BY DISCONTINUOUS MAGNETIZATION. 

 BY J. BOEGMANN. 



It follows from the experiments of Joule, Van Breda, Grove, 

 Edlund, Petruschewsky, Jamin and Eoger, Villari, Cazin, Herwig, 

 and Trowbridge, that heating takes place in iron w T hen it is exposed 

 to continuously interrupted magnetization. These experiments 

 nevertheless leave it open to doubt whether the heating in question 

 is a direct result of the magnetization, or whether it is simply the 

 result of the development of induction- currents in the mass of the 

 iron when the magnetization is interrupted. To solve this ques- 

 tion, the author made a series of simultaneous experiments with 

 iron and copper tubes of equal dimensions and under the same 

 conditions. Two glass tubes, 500 centim. in length and 4*5 centim. 

 in the clear, formed the reservoirs of air-thermometers ; in one 

 glass tube was placed copper tubes slit lengthwise, and in the other 

 iron tubes also slit. The increase of temperature of the air in 

 these glass tubes was determined by the sinking of the naphtha in 

 the two limbs of a manometer in comparison with the level of the 

 naphtha in a third limb ; the latter was connected with a reservoir 

 of great capacity, which was immersed in a large vessel of water in 

 order to eliminate the influence of the pressure of the air. These 

 glass tubes were surrounded by others of the same length but 

 larger diameter. The space between the tubes was filled with run- 

 ning water of the temperature of the room. The reservoirs thus 

 constructed were placed inside magnetizing spirals made of stout 

 copper wire (2 millim. diameter and 540 turns) coiled on thick paper 

 tubes. The magnetizing spirals were surrounded by induction- 

 spirals of fine wire. These spirals could be alternately connected 

 by means of a commutator with a Weber's electrodynamometer. 

 The two magnetizing spirals and the two induction-spirals were 

 exactly alike. Both spirals were inserted in the common circuit 

 of a battery of 4 to 10 PoggendorfPs elements. The breaking, 

 and change of direction of the magnetizing current, were effected 

 by special commutators which were constructed like those in the 

 Gramme machine, and were moved by a clockwork by Eichens. By 

 means of this commutator the current could be opened 5, 10, 20 

 times in a second, or its direction could be altered as often. From 



Phil. Mag. S. 5. Vol. 17. No. 107. May 1884. 2 E 



