Intelligence and Miscellaneous Articles. 301 



6. Copper pyrites, which was made to underga such a decompo.. 

 sition that its surface became adorned with the fine colours pre- 

 sented by iridescent copper pyrites. if • u i. 



When I commenced, thirty years ago, occupying myself with the 

 reproduction of mineral substances by the concurrence of the elec- 

 trical forces with those of the affinities, it was objected agamst me 

 that nature did not make use of voltaic couples. This objection 

 did not appear to me to be of a serious nature. I showed that 1 

 sometimes arrived at the same end without the intervention of a 

 couple by placing insoluble mineral substances in contact with various 

 solutions for several years. From this has resulted this new prin- 

 ciple in chemistry, that the insolubility of bodies is not absolute, 

 and that, in course of time, when they are ;in contact with certain 

 solutions, double decompositions take place, which give origin to 

 crystallized compounds similar to those found in metalliferous strata. 

 — Comptes Rendus, Dec. 15, 1856, p. 1101. 



TWINKLING OF THE STARS. 



The stars twinkled much at Brighton on the evening of the 16th 

 of March. Sirius and Aldebaran were in sight; and on pass- 

 ino- the axis of the eyes across them so as to produce a changing 

 place for their image on the retina, it was seen that the difference 

 due to twinkling was so great as at certain moments to cause the 

 apparent extinction of the stars. A mirror was therefore held in the 

 hands so as to send a reflected image of the selected star to the eye, 

 and then the mirror was moved in such a manner as to throw the 

 imao-e of the star into a line or a circle, which could easily be done. 

 Upon examining the brightness of the star image at the moment 

 when it was reflected from different parts of the moving mirror, the 

 light was seen to differ enormously, and very frequently, indeed, to 

 be replaced entirely by darkness. In fact, the successive phases of 

 the star which, being seen in one direction, gave a continual but 

 wavering light, were now separated into their luminous and their 

 ab'^olutely dark conditions ; and thus the effect of twinklings made 

 far more manifest than by the ordinary mode of observation. Ihe 

 apparent extinctions were not for long together; but they oftencut 

 up a circular path of light of about 10 degrees angular space into 

 six, seven, or eight parts, separated by short dark intervals wijjout 

 sensible light. ■^- *^- 



NOTE ON THE DENSITY AND THE MASS OF COMETS. 

 BY M. BABINET. 

 All astronomers are agreed that the mass and density of comets 

 are very small, and that their attraction cannot produce any sensible 

 effect upon the movements of the planetary bodies. We shall see 

 that from the effects observed, combined with the laws of optics, we 

 may deduce the conclusion that the direct shock of one of these 



