x THE STARRY HEAVENS 411 



no light which falls on the plate, however 

 faint, is lost ; it is taken in and stored up. 

 In an hour the effect is 3600 times as great 

 as in a second. By exposing the photographic 

 plate, therefore, for some hours, and even on 

 successive nights, the effect of the light is as 

 it were accumulated, and stars are rendered 

 visible, the light of which is too feeble to be 

 shown by any telescope. 



The distances and magnitudes of the 

 Stars are as astonishing as their numbers, 

 Sirius, for instance, being about twenty times 

 as heavy as the Sun itself, 50 times as 

 bright, and no less than 1,000,000 times as 

 far away ; while, though like other stars it 

 seems to us stationary, it is in reality sweep- 

 ing through the heavens at the rate of 1000 

 miles a minute ; Maia, Electra, and Alcyone, 

 three of the Pleiades, are considered to be 

 respectively 400, 480, and 1000 times as bril- 

 liant as the Sun, Canopus 2500 times, and 

 Arcturus, incredible as it may seem, even 

 8000 times, so that, in fact, the Sun is by 

 no means one of the largest Stars. Even 

 the minute Stars not separately visible to the 



