COMETS. 27 



the shades of light and colour during the transition from 

 one day to the other. Can anything be conceived more 

 gorgeous ? no shadow, but every object tinted with a com- 

 bination of colours of the most brilliant hues ! Triple, 

 quadruple, and multiple stars are known in abundance, but 

 all probably optically so, and not in any way connected with 

 each other by attraction. Others of the stars are called 

 " variable," they are those whose light gradually diminishes 

 and after a time regains its former brightness ; some of them 

 not only vary in brilliancy but in colour ; the cause of these 

 phenomena is totally unknown, and fortunate will he be who 

 discovers it ; it will be a great stride in the science of astro- 

 nomy, for at present everything proposed has been quite 

 inadequate to account for such phenomena. About 60 of 

 these variable stars are at present known, but others are 

 constantly being added to the list. Hind has discovered 

 twenty- one, Pogson seven, and other astronomers have taken 

 their share in discerning them. 



But, of all the heavenly bodies, none have excited so much 

 wonder, and in former times so much fear, as the Comets. 

 The orbits of these are for the most part in very eccentric 

 ellipses, some of them comprised within the limits of our 

 solar system, while those of others extend millions of miles 

 beyond it, so that they only reappear to us after hundreds 

 of years. The matter of Avhich these bodies is composed 

 is certainly not solid, as the smallest telescopic stars may be 

 seen through the very middle of it, although many thousand 

 miles in thickness. When comets approach the sun, their 

 substance appears to become more condensed, and therefore 

 to possess a greater power of reflecting light. The cause of 

 the "tails" which appear appended to comets when they 

 approach the sun is not known, but this tail extends always 

 in a direction from the sun, and passes over many degrees 

 of the heavens' space. As comets obey strictly the law of 

 gravitation, they must possess some amount of weight or 

 mass, however small it may be, and that it is inconceivably 

 small is proved by the fact of comets having passed close to 

 Jupiter, right amongst his four moons, without in any way 

 affecting or disturbing their well-known motions ; the 



