Astronomical and Nautical Collections, 



215 



nous undulations of different lengths are actually transmitted 

 with different velocities in the same refractive mediums, and 

 in variable proportions, of which the laws are yet entirely 

 unknown, but which seem to be very intimately related to 

 the chemical nature of the substances. But are we to infer 

 that there is any difference in the velocities of the different 

 rays of light in the pure ether, which occupies the celestial 

 space ? To this question it is difficult to reply with any cer- 

 tainty ; but the astronomical observations of Mr. Arago 

 appear to give us a negative answer. 

 [To be continued.] 



iii. Principal Lunar Occultations of the Fixed Stars in 

 the Months of May, June^Julyy and August, 1828; cal- 

 culated for the Royal Observatory at Greenwich, By 

 Thomas Henderson, Esq. 



