114 



Lord Rayleigh. 



It is a faot, as was found many years ago by Kundt and Warbnrsr* 

 (and as I have confirmed), that the viscosity of aqueous vapour is 

 but little greater than tbat of hydrogen. The numbers (relatively 

 to air) given by them are 0*5256 and 0*488. It is difficult to believe 

 that small traces of a foreign gas having a 6 per cent, greater 

 viscosity could produce an effect reaching to 10 per cent. 



In the recent experiments the hydrogen was prepared from 

 amalgamated zinc and sulphuric acid in a closed generator con- 

 stituting in fact a Smee cell, and it could be liberated at any 

 desired rate by closing the circuit externally through a wire resist- 

 ance. The generating vessel was so arranged as to admit of 

 exhaustion, and the materials did not need to be removed during 

 the whole course of the experiments. The gas entered the vis- 

 cosity chamber from below, and could be made to pass out above 

 through the upper tube (which served also to contain the fibre) into 

 the pump head of the T tippler. By suitable taps the viscosity 

 chamber could be isolated, when observations were to be com- 

 menced. 



The vibrations were started by a kind of galvanometer coil in 

 connection (through a key) with a Leclanche cell. As a sample 

 set of observations the following relating to hydrogen at atmo- 

 spheric pressure and at 58° F., which had been purified by passage 

 over fragments of sulphur and solid soda (without phosphoric 

 anhydride), may be given : — 



Observations on June 7, 1897. 





65 



4 











423 -7 



88 



9 



35s -3 



2 



•554 





401 3 



110 







3L2-4 



2 



•495 



0-059 



381-5 



128 



9 



271 -5 



2 



•434 



061 



364 -4 



144 



1 



235 5 



2 



37.2 



0-062 



349 -7 



158 



•6 



205-6 



2 



•313 



059 



336-8 



169 



•8 



. 178 '2 



2 



•251 



0-062 



325-7 



180 



6 



155 '!> 



2 



•193 



0-058 



315-7 



189 



8 



135-1 



2 



•131 



0-062 



307 -2 



197 



•8 



117 -4 



2 



•070 



061 



300-0 



204 



6 



102-2 



2 



•009 



0-061 



293-7 



210 



•6 



89 -1 



1 



•96.0 



059 



287-8 







77 2 



1 



•888 



0-062 



Mean log. dec. = 0-0604. 



The two first columns contain the actually observed elongations 

 upon the two sides. They require no correction, since the scale was 

 bent to a circular arc centred at the mirror. The third column 



* < Pogg. Ann.,' 1875, vol. 155, p. 547. 



