308 A nniversary Meeting. 



in investigating the nature of the new rays. Perhaps no outcome 

 of such inquiries has been more remarkable than the fact observed 

 by our Fellow Professor J. J. Thomson, that the rays have the power 

 of discharging electricity, both positive and negative, from a. body 

 surrounded by a non-conductor ; a mass of paraffin wax, for example, 

 behaving in their path for the time being like a conductor of elec- 

 tricity. 



It appears that Lenard had before observed the discharge of both 

 kinds of electricity through air by the rays with which he worked. 

 Lenard's rays, however, differ from Rontgen's in being deflectable by a 

 magnet, implying, in the opinion of most British physicists, that they 

 are emanations of highly electrified particles of ponderable matter, 

 while Rontgen's are regarded as vibrations in the ether. The question 

 naturally arises whether Lenard, in the observations referred to, may 

 not have been working with a mixture of Rontgen's rays and his 

 own. While points like these are still under discussion by experts, 

 we cannot but feel that the letter X, the symbol of an unknown 

 quantity, employed originally by Rontgen to designate his rays, is 

 still not inappropriate. 



I have before referred to Lippmann's beautiful demonstration 

 and discussion of colour photography in one of our meetings. 



Very important researches have been made both by Lord Rayleigh 

 and by Professor Ramsay into the physical properties of the new 

 substance, helium, discovered by Ramsay in the previous session. 

 Among their most striking results is the fact ascertained by Rayleigh 

 that the refractivity of helium is very much less than any previously 

 known, being only O146 ; between three and four times less than that 

 of hydrogen, the lowest that had before been observed, although 

 helium has more than twice the density of hydrogen. And equally 

 surprising is Ramsay's observation of the extraordinary distance 

 through which electric sparks will strike through helium, viz., 

 250 or 300 mm. at atmospheric pressure, as compared with 23 mm. 

 for oxygen and 39 for hydrogen. Such properties appear to indicate 

 that in helium we have to do- with an exceedingly remarkable 

 substance. 



The density of helium appears to be really slightly different 

 according to the mineral source from which it is obtained ; and this 

 circumstance seemis to give countenance to the opinion arrived at by 

 Lockyer and also by Runge and Paschen, from spectroscopic investi- 

 gation, that helium is not a perfectly pure gas. But whatever other 

 gas or gases may be mixed with it, they must be as inert chemically 

 as the main constituent ; for all Ramsay's elaborate attempts to 

 induce it, or any part of it, to combine with other bodies have 

 entirely failed. 



Professor Roberts- Austen, in the Bakerian lecture, brought before 



