paring their brightness with that of the 

 Sun, on the assumption that they give 

 out an amount of light not greatly differ- 

 ent from his. This method had, it seems 1 , 

 been first suggested by James Gregory ; 

 it was applied roughly by Huygens to 

 Sirius ; and it attracted the attention of 

 Lambert and later of Olbers, as well as 

 that of Michell. In MichelFs argument 

 the planet Saturn, whose size and distance 

 are known from the Newtonian theory, 

 and whose brightness relative to the Sun 

 could thus be estimated, was used as an 

 intermediary ; for it would be impossible 

 to compare directly the dazzling bright- 

 ness of the Sun with the amount of light 

 received from a star. These astronomers 

 all agree in assigning a parallax less than 

 half a second of arc to the brightest stars; 

 and this is in fact near the values that are 

 now known for the very few nearest stars, 

 which are thus at a distance from our 

 system of about a million times that of 



1 Grant, op. clt. p. 547. 

 IOO 



