VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 757 



Min. Sun. Bluish-green glass. 



Exper. 37. 6of 6'9| It stops 768 rays of heat, and 769 of 



5 76-f 71 ...7: 1|= .532. light. 



Min. Sun. Pale-blue glass. 



Exper. 38. 70| 70f The pale blue glass stops 812 rays 



5 76% 7H . • • 6 : li = .188. of heat, and only 684 of light. 



Min. Sun. Dark-blue glass. 



Exper. 39. 71 71 The dark-blue glass stops only 362 



5 76£ 743 . . . 5f : 3| = .638. rays of heat, and 801 of light. 



Min. Sun. Indigo glass. 



Expsr.40. 6l| ol| This glass stops 633 rays of heat, and 



5 67i 64 . . . 6^ : 2£ = .367. 9997, out of 10000 rays of light. 



Min. Sun. Pale-indigo glass. 



Exper. 41. 62 62 It stops 532 rays of heat, and 978 of 



5 67i 6'4| . . . 5f : 2| a .468. light. 



Min. Sun. Purple glass. 



Exper. 42. 613 613 It stops 583 rays of heat, and 993 of 



5 673 64J...6:2£ = .417. light. 



Min. Sun. Violet glass. 



Exper. 43. 62 J 62 J It stops 489 rays of heat, and 955 of 



5 68i 65} . . . 51 : 3 = .511. light. 



Transmission of Solar Heat through Liquids. — I took a small tube, 1-J- inch in 



diameter, fig. 16, and fixed a stop with a hole -§• inch wide at each end, on which a 



glass might be fastened, so as to confine liquids. The inner distance, or depth of 



the liquid, when confined, is 3 inches. Placing now the empty tube, with its 2 



end glasses fixed, on the transmitting apparatus, I had as follows : 



Min. Sun. Empty tube, and two glasses. These glasses, with the intermediate 



Exper. 44. 53 53 air, stop 542 rays of heat, and 204 of 



5 59 553 ... 6 : 23 = .458. light. 



Exper. 45. I filled the tube with well-water, Min. Sun. Well-water, 



and placed it on the transmitting apparatus. 52£ 52^ 



5 58| 55 . . . 6£ : 2-£ = .442. 



Here 2 glasses, with water between them, stopped 558 rays of heat. The same glasses, and water, 

 stop only 2 1 1 rays of light. If we were to deduct the effect of the empty machine, there would re- 

 main, for the water to stop, only 16 rays of heat, and 7 of light ; but it cannot be safe to make this 

 conclusion, as we are not sufficiently acquainted with the action of surfaces between the different 

 mediums on the rays of heat and light ; I shall therefore only notice the effect of the compound. 



Exper. 46. I filled now the tube with sea-water, Min. Sun. Sea-water, 

 taken from the head of the pier at Ramsgate, at 54| 54| 



high tide. 5 60 56 5£ : 13 = .318. 



The compound stops 682 rays of heat, and 288 of light. 



Min. Sun. Spirit of wine. 



Exper. 4,7. 51-| 514 The compound stops 612 rays of 



2-f = .388. heat, and 224 of light. 



Exper. 48. 52 52 This compound stops 739 rays of 



l£ = .261. heat, and 626 of light. 



Exper. 49. 56 56 This stops 794 rays of heat, and 996 



lj : 4= .206. rays of light. 

 Other liquids have also been tried ; but the experiments having been attended with circumstances that 

 demand a further investigation, they cannot now be given. 



Transmission of Solar Heat through Scattering Substances. 



Exper. 50. I rubbed one of the pieces of crown glass, mentioned in the 26th experiment, on fine 

 emery laid on a plain brass tool, to make the surface of it rough, which, it is well known, will occasion 



