100 



is employed, furnished with three delicate threads fastened 

 in a particular way to the objective of the telescopic 

 tube. 



Our universe is so immense that those millions of 

 versts which the planets have traversed since the starry 

 heavens have been observed through telescopes present 

 in all a distance comparatively insignificant, and this- 

 circumstance presents the chief difficulty which astronomy 

 encounters. Owing to this two stars having nothing in 

 common but happening to be at the time of observation 

 on the same straight line, appear as a double star and 

 only after long watching they are discriminated by their 

 increasing distance from one another. Such bodies are 

 called by astronomers optical double stars to distinguish 

 them from real or physical double stars. Herschel in his 

 investigations was extremely cautious in drawing conclu- 

 sions, and it was long before he declared himself con- 

 vinced of the existence of any real tie. His first calcula- 

 tions were made in the constellation of Orion and after 

 this a succession of observations in other constellations 

 led him to the conviction that the law of gravitation 

 operated outside as well as inside our solar system. 



We have already discussed the law of gravitation and 

 assigned this operative principle not to a fortuitous cosmic 

 fatality but to the intelligence of the cosmic spheres. This 

 cosmic relation, observable and demonstrable within our 

 system, in Herschel's opinion is universal. 



The Russian astronomers Otto Stroove and his son 

 William, the immediate successors of Herschel in this field 

 of research, beginning their investigations at Dorpat in 

 1813, with inadequate instruments, removed subsequently 

 to the Pulkovo Observatory where, in conjunction, they 

 observed more than 12000 stars from the first to the 

 eighth magnitude. Of this number 3112 were recognised 

 as double. The catalogue was published in 1827. 



William Stroove arrives at certain conclusions regarding 

 the colour of double stars, their relative size and move- 

 ment. His European rival in the study of these stars was 



