of dark Heat-rays by Gases and Vapours. 



17 



of the third three, and compare with the middle three, and so 

 also of the second and fourth with the middle three, we obtain 

 for J:— 



In vacuo... 100-00 99*95 100*00 99-75 



In air 99-85 99-56 99-78 99*49 



or, as mean result, that of 100 incident rays 99*78 pass 

 through. The difference between these numbers is unques- 

 tionably not more than the unavoidable errors of observation. 



II. Moist Air. 













Deflec- 









Name and 



pressure 



of vapour. 



R . 



Beversal-points. 



R,. 



tion in 

 divi- 

 sions 



of the 



scale. 



Mean. 



J. 



Pv 



Pr 



\Pv 



Pi- 



CO 



Pure dry air 

 at atmosphe- 

 ric pressure. 



66 

 65 

 63 



673 

 662 

 661 



524 

 525 

 523 



655 

 654 

 650 



590 

 589 

 594 



611-1 

 610-5 

 609-7 



545-1 

 545-5 

 546 7 



1545-8 



100-00 



CO 



Aqueous 



vapour 



7'4 millims. 



64 

 65 



66 



688 

 695 

 698 



523 



523 



526 



658 

 660 

 663 



592 

 590 

 596 



613-4 

 613-4 

 617-4 



549-4 

 548-4 

 551-4 



I 5497 



100-71 



OS 



Pure dry air 

 at atmosphe- 

 ric pressure. 



64 

 67 

 65 



693 

 693 

 694 



520 

 525 

 524 



661 



663 

 661 



594 

 596 

 599 



614-7 

 617-3 

 617-1 



550-7 

 550-3 



552-1 



I 551-0 



100-95 



11 



Aqueous 



vapour 



7'4 millims. 



QQ 

 65 

 66 



696 

 684 

 683 



524 

 525 



527 



664 

 661 

 660 



594 

 593 

 596 



616-9 

 615-3 

 6161 



5509 



550-3 

 5501 



I 550-4 



100-84 



GO 

 JI 



Aqueous 



vapour 



7 - 4 millims. 



66 

 64 

 69 



693 

 692 

 701 



520 

 521 



528 



660 

 658 

 663 



583 



582 

 587 



610-5 

 6096 

 614-5 



544-5 

 545-6 

 545-5 



1 545-2 



99-87 



Pure dry air 

 at atmosphe- 

 ric pressure. 



63 

 62 

 62 



693 



680 

 686 



522 

 525 

 518 



658 

 655 

 654; 



583 

 583 

 577 



610-0 

 609 

 605-3 



547-0 

 547 

 5433 



1 545-8 



100-00 



OS 

 I— 1 



II 



Aqueous 



vapour 



7*4 millims. 



66 

 69 

 66 



697 

 707 

 697 



526 



531 



525 



1 



660 1 

 672 

 660 . 



579 



587 

 579 



610-3 

 619-8 

 610-2 



544-3 

 550-8 

 544-2 



1 546-4 



100-11 



Arranged in the same way as before, we have for J: — 



Air 100-00 100-00 100-00 



Aqueous vapour... 100-24 100-17 99-99 



or, as mean result, that of 100 incident rays 100-20 emerge. 

 Hence the result of these experiments is that moist air does 

 not perceptibly absorb the heat-rays from a source at 100° C. 

 No imaginable source of error has here been left out of ac- 

 count. The arrangement for filling with moist air was varied, 

 the air allowed to stand for a long time over the water in the 

 Phil. Mag. S. 5. Vol. 11. No. 65. Jan. 1881. C 



