On the MOTION of LIGHT. nr 



Thus it appears that the water telefcope muft have the fame 

 pofition with the common telefcope, or that both of them muft 

 always be directed to the real place of the terreftrial object. 



It will alfo eafily appear, that when the image of a fixed flar 

 is formed upon the interfeclion of the crofs wires in the eye- 

 pieces of a common telefcope, and a telefcope filled with water, 

 the two telefcopes will have the fame pofition, and will indicate 

 the fame aberration of the fixed flars. For, by the fame rea- 

 foning, it appears that the water telefcope at A muft have the 

 pofition AB, and the aberration OAD is the fame with that ob- 

 ferved with a common telefcope. 



With this application of the general propofition I fhall con- 

 clude this paper, referving a farther account of the fubject for 

 another opportunity, if the Society fhall think it worthy of 

 their attention. 



XII, 



