1908.] Anniversary Address by Lord Rayleigh. 5 



But though I may use a little my privilege of grumbling over details, I hope 

 I shall not be misunderstood as undervaluing the progress made in recent 

 years, which, indeed, seems to me to be very remarkable and satisfactory, 

 regarded from the scientific point of view. On the other hand I cannot help 

 feeling misgivings as to the suitability of the highly specialised mathematics 

 of the present day for a general intellectual training, and I hope that a careful 

 watch may be maintained to check, in good time, any evil tendencies that 

 may become apparent. 



Among the notable advances of the present year is the liquefaction of 

 helium by Professor Onnes of Leiden. It is but a few years since Sir J. Dewar 

 opened up a new field of temperature by his liquefaction of hydrogen, and 

 now a further extension is made which, if reckoned merely in difference of 

 temperature, may appear inconsiderable, but seen from the proper 

 thermodynamical standpoint is recognised to be far-reaching. The explora- 

 tion of this new field can hardly fail to afford valuable guidance for our 

 ideas concerning the general properties and constitution of matter. Professor 

 Onnes' success is the reward of labours well directed and protracted over 

 many years. 



The discovery and application by Rutherford and Geiger of an electrical 

 method of counting the number of a-particles from radio-active substances 

 constitutes an important step, and one that appears to afford better determina- 

 tions than hitherto of various fundamental quantities. It would be of interest 

 to learn what interpretation is put upon these results by those who still 

 desire to regard matter as homogeneous. 



Another very interesting observation published during the year is that of 

 Hale upon the Zeeman effect in sun-spots, tending to show that the spots are- 

 fields of intense magnetic force. Anything which promises a clue as to the 

 nature of these mysterious peculiarities of the solar surface is especially 

 welcome. Until we understand better than we do these solar processes, on 

 which our very existence depends, we may do well to cultivate a humbler 

 frame of miud than that indulged in by some of our colleagues. 



A theoretical question of importance is raised by the observations of 

 ISTordmann and Tikhoff showing a small chromatic displacement of the 

 phase of minimum brightness in the case of certain variable stars. The 

 absence of such an effect has been hitherto the principal argument on 

 the experimental side for assuming a velocity of propagation in vacuum 

 independent of frequency or wave-length. The tendency of the observations- 

 would be to suggest a dispersion in the same direction as in ordinary 

 matter, but of almost infinitesimal amount, in view of the immense distances 

 over which the propagation takes place. Lebedew has pointed out that 



