160 ANNUAL OF SCIENTIFIC DISCOVERY. 



of light and the sun's parallax, which promises important results. 

 By means of a newly-devised instrument he has ascertained that the 

 velocity of light is notably less than has been supposed. Instead of a 

 velocity of 308,000,000 of metres in a second, he estimates it as 

 298,000,000. If this be correct, the sun's parallax is 8.86", instead 

 of 8.5 1". Thus the mean distance of the sun from our earth is dimin- 

 ished by about -$. 



DISPERSION OF LIGHT. 



M. Kaclan, writing to the Paris Cosmos upon the results of 

 Cauchy, and citing his formulas, observes : "It results from these 

 foramlse that the velocity of a luminous ray depends, in general, 

 upon its color ; and that the unequal velocities of the different rays 

 of the spectrum are the cause of their dispersion by the prism." 



THE FORMATION OF HALOS. 



Sir John Herschel has devised an elegant mode of illustrating the 

 action of minute refracting spheres. He mounts the spores of the 

 common puff-ball in a film of oil between two pieces of glass. When 

 these are held close to the eye, and a candle viewed through them, 

 beautiful concentric halos appear. 



NEW OPTICAL EXPERIMENT. 



Mr. Slack calls attention to concentric circles of light, exquisitely 

 marked by fine black, intersecting lines, which may be seen by taking 

 a stout glass tube, about one-eighth of an inch in diameter and six or 

 eight inches long, holding it horizontally opposite the flame of a can- 

 dle, and looking at the light through it. A piece of paper rolled 

 round the tube shuts out all unnecessary illumination, and makes the 

 phenomenon more clear. 



IMPROVEMENT IN THE KALEIDOSCOPE. 



The following note addressed to the London Literary Gazette, by 

 Mr. J. A. Davis, suggests an improvement in the kaleidoscope, or, in 

 fact, in any instrument where combinations of colors are produced by 

 rotation : " Sir : If the pieces of glass used in a kaleidoscope were 

 cut in various regular forms, the effect of the instrument would 

 greatly be improved, and this by means of the duplication of sym- 

 metry or evenness, which can readily be understood by all who have 

 a competent knowledge of it. Every apparatus or instrument for 

 producing color by rotation of colored surfaces would be improved if 

 a conical glass vessel, the upper external part of which is silvered, 

 were fixed upon the spindle with its apex downwards, in which a 

 number of pieces of various colored glass were placed, and under- 

 neath it a mirror at a proper angle were fixed. Upon the middle 

 being rotated, the pieces of glass would, by centrifugal force, be car- 

 ried towards, and in some cases against, the internal parts of the 

 cone, and be illuminated by the mirror beneath, and reflected by the 

 silvered parts of the vessel. The effect produced would be a very 

 beautiful one, a number of concentric colored rings being visible, the 



