[ 387 ] 
YII. On the Viscosity of Gases at High Exhaustions. 
By William Crookes, F.R.S. 
Received December 26, 1880,—Read February 17, 1881. 
[Plates 55-58.] 
Contents. 
Par. 
Introduction. 635 
The viscosity torsion apparatus... 638 
McLeod’s gauge for high vacua. 642 
Process of observation. Logarithmic decre¬ 
ment . 645 
Precautions necessary before exhausting to 
high points . 650 
Note on the viscosity of glass. 652 
Viscosity of air. 653 
Repulsive force of radiation in air. 655 
Calculating the zero-point for the swing pro¬ 
duced hy radiation . 656 
Plotted curves of the viscosity of air........ 658 
Mean free paths of the molecules . 661 
Resistance of air to the passage of an induc¬ 
tion spark. 663 
Viscosity of oxygen gas. 666 
Plotted curves of the viscosity of oxygen.... 668 
Repulsive force of radiation in oxygen. 670 
Viscosity of nitrogen gas. 671 
Comparison of the air curves with those of 
oxygen and nitrogen . 674 
Observations on the spectrum of nitrogen .. „ 675 
Repulsive force of radiation in nitrogen .... 676 
Viscosity of carbonic anhydride gas. 677 
Plotted curves of the viscosity of carbonic 
anhydride. 679 
Par. 
Repulsive force of radiation in carbonic an¬ 
hydride . 680 
Observations on the spectrum of carbonic 
anhydride. 681 
Viscosity of carbonic oxide gas .. 682 
Plotted curves of the viscosity of carbonic 
oxide. 684 
Repulsive force of radiation in carbonic oxide 685 
Observations on the spectrum of carbonic 
oxide. 686 
Viscosity of hydrogen gas. 687 
Plotted curves of the viscosity of hydrogen.. 690 
Repulsive force of radiation in hydrogen .... 691 
Proportion between the viscosities of air and 
hydrogen . 692 
Influence of foreign gas on the viscosity of 
hydrogen . 695 
Observations on the spectrum of hydrogen .. 698 
Influence of aqueous vapour on the viscosity 
of air. 699 
Plotted curve of the viscosity of moist air .. 701 
Explanation of the action of aqueous vapour 702 
Viscosity of kerosoline vapour. 705 
Discussion of results . 706 
The ultra-gaseous state of matter. 710 
Note on the Reduction of Mr. Crookes’s Experiments on the Decrement of the Arc of Vibration 
of a Mica Plate oscillating within a Bulb containing more or less Rarefied Gas. By 
Professor G. G. Stokes, Sec. R.S...page 435 
3 E 
MDCCCLXXXI. 
