of dark Heat-rays by Gases and Vapours. 



19 



measured with the same minute accuracy and care as the two 

 already given, since we hoped to draw conclusions on the rela- 

 tion between pressure and absorption. Nevertheless, from the 

 experiments with ether vapour, carbon dioxide, &c. this much 

 may be concluded with certainty, that the well-known law of 

 absorption J = 100e~^ 



does not apply here, since the coefficient x always becomes 

 smaller as the thickness d of the layer becomes smaller. Hence 

 the absorption is selective even with a source of heat atl00° C. 

 The results will be discussed at the end of this paper. 



I. 



1. Methyl Alcohol. 





Name and 



pressure of 



vapour. 



B . 



Reversal- points. 



R r 



Deflec- 

 tion, in 

 divi- 

 sions 

 of the 

 scale. 



Mean. 



J. 



Pv 



Pv 



Pi- 



Pi- 



i — i 



d 



00 



II 



Pure dry air. 



377 

 375 

 388 



745 

 739 

 751 



631 

 635 



651 



685 

 682 

 697 



654 

 655 

 664 



665-4 

 664-6 

 678-2 



288-4 

 289-6 

 290-2 



289-4 



100-00 



op 

 ll 



CHA 



44 rnillims. 



366 

 370 



370 



730 

 738 

 734 



623 

 630 

 624 



674 

 681 



677 



641 



647 

 645 



654-4 

 660-9 

 657-3 



288-4 

 290-9 

 287-3 



I 288-9 



9982 



00 



II 



Pure dry air. 



221 

 220 

 219 



440 

 438 

 433 



368 

 368 

 368 



343 

 340 

 339 



384 

 380 

 381 



360-6 

 357-8 

 357-6 



139-6 

 137-8 

 138-6 



1 138-7 



100-00 



00 

 II 



CH 4 0, 



44 rnillims. 



217 

 218 

 217 



431 



433 

 433 



364 

 366 

 363 



338 

 338 

 337 



377 

 379 

 376 



355-2 

 356-1 

 354-2 



138-2 

 138-1 

 137-2 



1 137-8 



99-42 



2. Formic Acid. 



op" 

 6 



00 



Pure dry air. 



325 

 326 

 324 



565 

 571 

 569 



486 

 493 

 489 



519 

 520 

 514 



498 

 497 

 496 



506-5 

 507-7 

 505-7 



181-5 

 181-7 

 181-7 



181-6 



100-00 



op 



ll 



CH 2 2 , 



145 rnillims. 



327 



326 

 326 



564 

 567 

 565 



483 



486 

 484 



520 

 518 

 520 



495 

 496 

 495 



505-4 

 505-2 

 505-5 



178-4 

 1792 

 179-5 



1 179-0 



98-55 



3. Chloroform. 



op 



o 

 00 



II 



Pure dry air. 



320 

 322 

 319 



559 

 560 



561 



476 

 479 

 474 



514 

 515 

 513 



489 

 492 

 490 



499-2 

 501-2 

 498-6 



179-2 

 1792 

 179-6 



1 179-3 



100-00 



op 



IT 



CHC1 3 , 

 70 millims.(?) 



315 



320 

 320 



550 

 560 

 561 



470 



477 



476 



508 

 513 

 511 



483 

 491 



489 



493-2 

 499-5 

 4976 



178-2 

 179-5 

 177-6 



1 178-4 



99-50 



C 2 



