84 LIGHT SCIENCE FOR LEISURE HOURS. 



near the three seen by Huyghens. The four form the 

 celebrated trapezium, an object interesting to the pos- 

 sessors of moderately good telescopes, and which has 

 also been a subject of close investigation by professed 

 astronomers. Besides the four stars seen by Cassini, 

 there have been found five minute stars within and 

 around the trapezium. These tiny objects seem to 

 shine with variable brilliancy ; for sometimes one will 

 surpass the rest, while at others it will be almost 

 invisible. 



After Cassini's discovery, pictures were made of the 

 great nebula by Picard, Le Grentil, and Messier, These 

 present no features of special interest. It is as we 

 approach the present time, and find the great nebula 

 the centre of quite a little warfare among astronomers 

 now claimed as an ally by one party, now by their 

 opponents that we begin to attach an almost romantic 

 interest to the investigation of this remarkable object. 



In the year 1811, Sir W. Herschel announced that 

 he had (as he supposed) detected changes in the Orion 

 nebula. The announcement appeared in connection 

 with a very remarkable theory respecting nebulae gene- 

 rally Herschel's celebrated hypothesis of the conver- 

 sion of some nebulae into stars. The astronomical 

 world now heard for the first time of that self-luminous 

 nebulous matter, distributed in a highly attenuated 

 form throughout the celestial regions, which Herschel 

 looked upon as the material from which the stars have 

 been originally formed. There is an allusion to this 

 theory in those words of the Princess Ida : 



