148 Dr Olbers on the Transparent/ of Space, 



The logarithm of which is = 0.7385524 



Log a = 6.7349604 — 10 



Log ^ = 4.0035920 

 a' z= 10083.05 



It is therefore at a distance equal to 10000 times that of Sirius. 

 Thus, a certain quantity of stars situated at this distance would 

 require to be accumulated close to one another, before, in a clear 

 and moonless night, our most perfect telescopes could render 

 this group visible as a pale nebulosity. 



Our atmosphere, illuminated by the full moon, has not even 

 -i— of its lustre, and this light suffices to render invisible to 

 the naked eye all the stars which are under the fourth or fifth 

 magnitudes. The following calculation shews at what distance 

 the stars have still a lustre equal to that of the ground of the 

 sky, in a night illuminated by the full moon. 



We have then, 



Log (300000 X 90000) = 10.4313638 

 The log of which is =: 1.0183410 



Log«= 6.7349604—10 



Log^=: 4.2833806 

 Therefore ^- 19203.5 



Let us still calculate the lustre of a star, which is placed at 

 30,000 times the distance of Sirius ; then 

 Log a: = 4,4771213 

 Log a = 6,7349604—10 



Log a^=r: 1.2120817 

 The number of which is 16.29602 



Therefore log t = — 16.29602 



The number of which is 1977100000 millions, and expresses 

 how many times the absolute lustre of the star is weakened at this 

 distance. To form a conception of this relation the more easily, 

 it may be remarked, that the lustre then preserved by the star 



