$6 Dr. Herschel on the Power of 



bright, at whatsoever distance the observer be placed that views 

 it, the sun also, at the distance of Saturn, or still farther from us, 

 must be as bright as it is in its present situation. Nay, it may be 

 urged, that in a telescope, the different distance of stars can be of 

 no account with regard to their brightness, and that we must 

 consequently be able to see stars which are many thousands of 

 times farther than Sirius from us ; in short, that a star must be 

 infinitely distant not to be seen any longer. 



Now, objections such as these, which seem to be the imme- 

 diate consequence of what has been demonstrated by mathema- 

 ticians, and which yet apparently contradict what I assert in this 

 paper, deserve to be thoroughly answered. 



It may be remembered, that I have distinguished brightness 

 into three different sorts.* Two of these, which have been dis- 

 criminated by intrinsic and absolute brightness, are, in common 

 language, left without distinction. In order to shew that they 

 are so, I might bring a variety of examples from common con- 

 versation ; but, taking this for granted, it may be shewn that 

 all the objections I have brought against my theory have their 

 foundation in this ambiguity. 



The demonstrations of opticians, with regard to what I call 

 intrinsic brightness, will not oppose what I affirm of absolute 

 brightness ; and I shall have nothing farther to do than to shew 

 that what mathematicians have said, must be understood to 

 refer entirely to the intrinsic brightness, or illumination of the 

 picture of objects on the retina of the eye : from which it will 

 clearly follow, that their doctrine and mine are perfectly recon- 

 cileable ; and that they can be at variance only when the am- 

 biguity of the word brightness is overlooked, and objections, 



* See page 52. 



