758 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



the transmitted light to be scattered in all directions. Supposing that it would have the same effect on 



heat, I tried the transmitting capacity of the glass, 



by exposing it with the rough side towards the Min. Sun. Crown glass. 



sun, over one of the transmitting holes of the 67 67 



apparatus. 5 74 70| . . . 7 : 3| = .536. 



The glass so prepared stops 464 scattered rays of heat, and 854 of light. Now, as the same glass, in 

 its polished state, transmitted 259 rays of heat, and 203 of light, the alteration produced in the texture 

 of its surface acts very differently on these 2 principles ; occasioning an additional stoppage of only 205 

 rays of heat, but of 651 rays of light. 



Exper. 51. One of the pieces of coach glass, Min. Sun. Coach glass, 



mentioned in the 27th experiment, was prepared 663 66% 



in the same manner. 5 73 \ 69^ ... 7 : 3 = .429- 



It stops 571 scattered rays of heat, and 885 of light ; so that the fine scratches on its surface, made by 

 the operation of emery, have again acted very differently on the rays of heat, and of light, occasioning 

 an additional stoppage of 375 of the former, but of no less than 7 1 7 of the latter. 



Etpcr. 52. I took another of the pieces of crown Crown glass ; 



glass, mentioned in the 26th experiment, and Min. Sun. both sides rubbed on emery, 

 rubbed both sides on emery. 69? 69^ 



5 75\ 71} h. 6 : 2 = .333. 



The glass thus prepared, stops 667 scattered rays of heat, and 932 of light. 

 Exper. 53. Another piece of coach glass, one of Coach glass ; 



those that were mentioned in the 27th experiment, Min. Sun. both sides rubbed on emery, 

 was prepared in the same manner. 69% 69% 



5 75$ 7lJ...6-L:lA = .265. 



It stops 735 scattered rays of heat, and 946 of light. 



Exper. 54. I placed now the coach glass, one side of which had been rubbed on emery, on the trans- 

 mitting hole, and over it the crown glass prepared 



in the same manner, both with the rough side to- Crown glass, and. coach glass ; 



wards the sun ; but 2 slips of card were placed be- Min. Sun. one side of each rubbed on emery, 

 tween the glasses, to keep them from touching 67 67 



each other. 5 73*- 69 ... 6*- : 2 = .302. 



These glasses stop 698 scattered rays of heat, and 969 of light. 



Exper. 55. I placed now the coach glass, with Coach glass, and crown glass ; 



both sides rubbed on emery, on the transmitting Min. Sun. both sides of each rubbed on emery, 

 hole, and over it the crown glass prepared in the 69% 69| 



same manner, with 2 slips of card between them, 5 75% 70^ . . . 6£ : I5 = .200. 



to prevent a contact. 



These glasses stop 800 scattered rays of heat, and 979 of light. 



rCrown glass ; the rough side to the sun. 

 Exper. 56. I used now all the 4 glasses j placing Min. Sun. \ g^S 5 . ^gh on both sides. 

 them as follows, and putting slips of card between V_Coach glass ; ditto, 



them, to prevent a contact. : 57% o7k 



5 62I 58| ...54,: | = .146. 



These 4 glasses stop no more than 854 scattered rays of heat, and 99$ of light. 

 Exper. 17. I used now a piece of glass of an 

 olive colour, burnt into the glass, in the manner Min. Sun. Olive-coloured glass, 

 that glasses are prepared for church windows, 69 69 



which transmits only scattered light. 5 76% 70j . . . 7| : 1| = .l6l 



This glass stops 839 scattered rays of heat, and 984 of light. 



Min. Sun. Calcined talc. This substance stops 867 scattered 



Exper. 58. 5 If 51* rays of heat, and so much light that 



5 55± 5 1-Z- . . . 3f : J- = . 1 33. the sun cannot be perceived through it.* 



Min. Sun. White paper. 

 Exper. 59. 63 63 This substance stops 850 scattered 



5 68 63| . . . 5 : I = .150. rays of heat, and 994 of light. 



Min. Sun. Linen. 



Exper. 60. 63 63 "White linen stops 916 scattered rays 



5 69 63^. . . . 6 : £ = .0833. of heat, and 952 of light. 



* See the 175th experiment. 



