cf the invijible Rays of the Sun. 13 



No - V No - ?• No - 3-| Here the thermometer No. I 

 4 f 4°* 4o ^ ro f e 8 decrees in 10 mi- 



55i ^i 48 r nutes> 

 57 49 ■ 48^ J 



By way of not lofing time, in order to connect thefe laft 

 ohfervations the better together, I did not bring back the 

 thermometer No. 1, to the temperature of the room, being 

 already well acquainted with its rate of ihowing, compared 

 to that of No. 2, but went on to the next experiment, by 

 withdrawing the ftand, till the whole ball of No. 1 was 

 completely out of the fun's vifible rays, yet fo as to bring 

 the termination of the line of the red colour as near the out- 

 fide of the ball as could be without touching it. 

 No. 1. No. 2. No* 3.-\ Here the thermometer No. 1, 



rofe, in 10 minutes, an- 

 other degree higher than 

 in its former fituation it 

 49 ' £ J could be brought up to ; 

 and was now 9 degrees above the ftandard. The ball of this 

 thermometer, as has been noticed, is exactly half an inch in 

 diameter ; and its centre, therefore, was i inch beyond the 

 vifible illumination, to which no part of it was expofed. 



It would not have been proper to compare thefe laft obferv- 

 ations with thofe taken at an earlier period this morning, in 

 order to obtain a true maximum, as the fun was now more 

 powerful than it had been at that time ; for which reafon I 

 caufed the line of termination of vifible light, now to fall 

 again juft i inch from the centre of the ball, and had the 

 following refult : 



And here the thermometer 

 No. 1, rofe, in 16 minutes, 

 8jr degrees, when its cen- 

 tre was : inch out of the 

 vifible ravs of the fun. 

 Now, as before we had a rifing of nine degrees, and here 8^, 

 the difference is almoft too trifling to fuppofe that this latter 

 fituation of the thermometer was much beyond the maximum 

 of the heating power; while, at the fame time, the experi- 

 ment fufficiently indicates that the place inquired after, need 

 not be looked for at a greater diitance. 



. 4 It 



