Intelligence and Miscellaneous Articles. 573 



on considering the circumstances of that experiment, I have remarked 

 a cause of compensation which must render the effect of the motion 

 imperceptible. This cause consists in the reflexion which the light 

 undergoes in that experiment ; in fact it may be demonstrated, that 

 when two rays have a certain difference of course, that difference 

 is changed by the effect of the reflexion upon a mirror in motion. 

 On calculating separately the two effects in the experiment of M. 

 Babinet, it is found that they have values sensibly equal with con- 

 trary signs. 



This explanation renders still more probable the hypothesis of an 

 alteration of velocity, and an experiment made with water in motion 

 appears to me completely appropriate to decide the question with 

 certainty. 



The success of the experiment seems to me to render the adop- 

 tion of Fresnel's hypothesis necessary, or at least the law which he 

 found for the expression of the alteration of the velocity of light by 

 the effect of motion of a body ; for although that law being found 

 true may be a very strong proof in favour of the hypothesis of 

 which it is only a consequence, perhaps the conception of Fresnel 

 may appear so extraordinary, and in some respects so difficult, to 

 admit, that other proofs and a profound examination on the part of 

 geometricians will still be necessary before adopting it as an ex- 

 pression of the real facts of the case. — Comptes Rendus, Sept. 29, 

 1851. 



ON THE FORMATION OF ANHYDROUS CRYSTALLIZED ALUM. 

 BY THE PRINCE OF SALM-HORSTMAR. 



Alumina, obtained by precipitating ammonia-alum by ammonia 

 and heating the precipitate to redness, was fused with four times i;s 

 weight of bisulphate of potash ; on treatment of the fused mass with 

 water, six-sided tables which did not doubly refract light were left, 

 and on analysis were found to consist of anhydrous alum. — Journ. 

 fiir Prakt. Chem. vol. Hi. p. 319. .*c 



ON THE COMPOSITION OF THE GASES EVOLVED ON THE PRODUC- 

 TION OF COKE FROM COAL. BY M. EBELMEN. 



The question might arise, whether in the formation of coke from 

 coal in a furnace, the air which enters the furnace gives up its 

 oxygen to the matters which are evolved in the gaseous state, or to 

 the solid carbon ; and again, whether the oxygen forms carbonic 

 oxide or carbonic acid. Ebelmen examined the composition of the 

 gases of the coke-ovens at Seraing, and found that more than two- 

 thirds of the hydrogen of the coal is burned, the remainder existing 

 in the evolved gaseous mixture. The quantity of carbonic acid is 

 three times that of the carbonic oxide. — Comptes Rendus, vol. xxxii, 

 p. 92. 



Phil Mag, S. 4. No. 14. Suppl Vol. 2. 2 Q 



