penetrating into Space by Telescopes. 81 



hours, in which it is hardly possible to put a limit to magni- 

 fying power. But such valuable opportunities are extremely 

 scarce; and, with large instruments, it will always be lost labour 

 to observe at other times. 



As I have hinted at the natural limits of magnifying power, 

 I shall venture also to extend my surmises to those of pene- 

 trating power. There seems to be room for a considerable 

 increase in this branch of the telescope ; and, as the penetrating 

 power of my 40-feet reflector already goes to 191,69, there can 

 hardly be any doubt but that it might be carried to '500, and 

 probably not much farther. The natural limit seems to be an 

 equation between the faintest star that can be made visible, by 

 any means, and the united brilliancy of star-light. For, as the 

 light of the heavens, in clear nights, is already very considerable 

 in my large telescope, it must in the end be so increased, by 

 enlarging the penetrating power, as to become a balance to 

 the light of all objects that are so remote as not to exceed in 

 brightness the general light of the heavens. Now, if P be put 



for penetrating power, we have v / — — = A = 10 feet 5,2 



inches for an aperture of a reflector, on my construction, that 

 would have such a power of 500. 



But, to return to our subject ; from what has been said before, 

 we may conclude, that objects are viewed in their greatest per- 

 fection, when, in penetrating space, the magnifying power is 

 so low as only to be sufficient to shew the object well; and 

 when, in magnifying objects, by way of examining them mi- 

 nutely, the space-penetrating power is no higher that what will 

 suffice for the purpose ; for, in the use of either power, the inju- 

 dicious overcharge of the other, will prove hurtful to perfect 

 vision. 



mdccc M 



