OF THE COSMOS. RAYS AND SPU1UOUS DISCS. 109 



laws in respect to their relative distribution as have hitherto 

 been recognised, we have still to consider some particular 

 appearances presented by them to our sense of vision ; viz. 

 their rays, their apparent unreal diameters, and the di- 

 versities of colour of different stars. Of the apparent rays, 

 which differ in number, position, and length, as seen by 

 every individual, I have already spoken when treating of the 

 subject of Jupiter's satellites. ( 204 ) Indistinct vision (la 

 vue indistincte) arises from various organic causes, dependent 

 on the spherical aberration of the eye, on diffraction at 

 the margins of the pupils or at the eye-lashes, and on the 

 irritability of the retina spreading more or less widely from a 

 stimulated point. ( 205 ) I see very regularly, in stars from 

 the 1st to the 3d magnitude, eight rays, at angles of 45. 

 As, according to Hassenfratz, these rays are caustics on the 

 crystalline, formed by the intersection of the refracted rays, 

 they move according as the spectator inclines his head to 

 either side. ( 206 ) Some of my astronomical friends see three 

 or at most four upward, and no downward rays. It has always 

 appeared to me remarkable that the ancient Egyptians inva- 

 riably give to stars five rays only (at every 72) ; so much so, 

 that, according to Horapollo, a star signifies in hieroglyphics 

 the number 5. ( 2 7) 



These rays disappear if the star is viewed through a small 

 hole made in paper with a needle (I have often observed 

 Canopus, as well as Sirius, in this manner) . The rays appear 

 in telescopic vision with high magnifying powers, when the 

 stars present themselves either as luminous points of more 

 intense light, or as extremely small discs. Although the less 

 degree of scintillation between the tropics gives a certain im- 

 pression of repose, yet the entire absence of rays, in viewing. 



