192 Dr. E. Bouty on the Magnetization of Steel by Currents. 



primaries. Hence one would expect that the obliquities of the 

 planets to their orbits would diminish as we go away from the 

 sun. It is believed (but the observations seem doubtful) that 

 Mercury and Venus are very oblique to their orbits ; and Mars 

 has an obliquity nearly the same as that of the earth. The 

 region of the asteroids is a blank ; and then we come to Ju- 

 piter, with a very small obliquity. 



The next in order is Saturn : and his case is unfavourable ; 

 for he is slightly more oblique to his orbit than is the earth. 

 Nevertheless it must be observed that he has a large number 

 of satellites , and some are very remote from him ? and his mean 

 density is very small ; hence, if the satellites can have affected 

 the obliquity in any case ? One would expect them to have done 

 so in that of Saturn. 



No light whatever is thrown on the case of Uranus, whose 

 axis is said to lie nearly in the plane of his orbit. 



XXYI. On the Magnetization of Steel by Currents. 

 By E. Bouty, Docteur es Sciences. 



[Concluded from p. 135.] 



III. Temporary and Permanent Magnetization of thin Needles 

 only slightly hardened. 



THESE experiments, like the foregoing, were made with 

 the steel wire used for spindles in clock-making ; but 

 instead of steeping the needles at a red-heat, they were used 

 in the state in which they were delivered by the maker — that 

 is to say, not tempered. Here rupture-experiments are out of 

 the question, and it is convenient to take as a starting-point, 

 not the study of the permanent magnetization, but that of the 

 temporary. 



The needles to be investigated are placed at a distance from 

 the galvanometer-needle equal to 50 or 60 centims. ; and the 

 operation is conducted according to the method employed in 

 the preceding section*. At this distance, and with the dimen- 

 sions of the needles used, Gauss's formula applies without 

 needing the introduction of the corrective terms, and one can 

 compare the moments of needles of different lengths without 

 knowing any thing a priori of the position of the poles. Let 

 us consider n needles of different lengths I, V, . . . } and submit 



* The quantity of magnetism being much greater in feebly hardened 

 needles than in the same needles strongly hardened, the employment of 

 long distances does not diminish the absolute values of the deflections 

 sufficiently to render the measurements uncertain in the present case, as it 

 did in that of the preceding section. 



