THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



APRIL 1882. 



XXVII. An Examination of Vacua. 

 By J. B. Haiotay, F.R.S.E., F..C.S* 



[Plate VI.] 



THE discovery detailed in a paper read before the Royal 

 Society f , that solids are capable of absorbing and fixing 

 large quantities of gases, led me to an examination of various 

 surfaces in contact with gases. It soon became apparent 

 that not only is there a closely adherent layer of gas on 

 every surface, as shown by Crookes and Liveing and Dewar, 

 but that the gas seems even at ordinary pressures to penetrate 

 into, or combine with, the surface of the glass, and that it is 

 with extreme difficulty that even a portion of this gas is 

 driven off, the greater portion remaining fixed even to the 

 softening-point of the glass. Experiments soon led me to the 

 conclusion that the estimates made as to the real extent of the 

 evacuation of spaces were fallacious; and a serious examination 

 of the extent of evacuation was attempted. There was also 

 in my mind the wish to test, if at all possible, the idea 

 held by Euler, and advocated by Grove and others, that 

 radiation may be propagated by ordinary matter, and not by 

 the luminiferous aether. The idea was, to evacuate a space as 

 perfectly as possible and subject it to intense cold, and then 

 test whether or not it would pass radiant energy. As it was 

 evident that the pressure of mercury vapour is quite appre- 

 ciable at ordinary temperatures, and is in itself quite sufficient 



* Communicated by the Author. 



t Proc. Eov. Soc. No. 214, 1881. 



Phil Mag. S. 5. Vol. 13. No. 81. April 1882. U 



