TRANSACTIONS OF SECTION A. 605 



moving to the second apex did not seem in accordance with Mr. Eddington's 

 determination that the stars of the first group were moving in streams, and that 

 the mean velocities of these streams were as 3:1. The investigation was not 

 concluded, but showed that stars of large proper motions had apparent drifts to 

 two points in the sky, but a difficulty was presented in the explanation of this 

 as due to two streams, 



7, The Reflecting Telescope and its Suitability fur Physical Reseaixh. 

 ■ By Sir Howaed Geubb, F.B.S. 



The author refen-ed to a Paper published by him some thirty-one years ago, in 

 which he pointed out the advantage of the reflecting telescope for many branches 

 of physical research, and predicted that the usefulness of the instrument would 

 be appreciated in course of time. For many years after this, instruments of the 

 reflecting type were not in favour either in Europe or America, but experience 

 of recent years of the use of reflectors in the hands of Huggins, Common, Roberts, 

 Wilson, and the astronomers at the Lick Observatory has practically demon- 

 strated the valuable qualities of such instruments for astrophjsical research. In 

 America especially many improvements in construction and mounting have been 

 introduced in recent years, which have helped largely to develop the powers and 

 convenience of the reflecting telescope. 



Notwithstanding the general impression that the practical limit of size for 

 large telescopes has been reached, and that further developments would be useless 

 on account of the limitations due to imperfections in our atmosphere, the obser- 

 vations' and investigations of American astronomers, who have expeinence of the 

 largest instruments, tend to show that, for physical research, not only would 

 instruments of greater light-grasping power be desirable, but that they are 

 absolutely necessary in order to carry through the work of physical research on 

 the most promising lines. 



Those who have had experience with large reflecting telescopes have therefore 

 devoted themselves in endeavouring to grapple with the diificulties which at 

 present hamper the usefulness of such instruments. 



This Paper discussed the various devices introduced by the astronomers at 

 Washington, Mt. Wilson, and other observatories possessing large reflectors to 

 overcome the hindrances to increase of aperture due to the want of homogeneity 

 in the air and calorific eff'ects, &c., and discussed the possibilities of increasing the 

 optical power in future instruments. 



MONDAY, SEPTEMBER 7. 



Discussion on the Theory of Wave-motion,^ opened by 



Professor Horack Lamb, F.R.S. 



[Plate vii.] 



It is understood that one of the chief objects of the discussion Is to promote 

 an alliance, or at all events a better understanding, between meteorologists on 

 the one hand and mathematicians on the other, more especially as to the theory 

 of atmospheric waves of various kinds. The need for some such understanding 

 is fairly manifest. There exists a considerable mathematical literature on the 

 subject of waves in fluids, but the theory is far from complete, and the established 

 results are subject to various qualifications which sometimes seriously limu their 

 practical application. It is possible that the theory might be extended in some 

 directions, with a view to meteorology ; but the mathematician is deterred from 

 embarking cu long and difficult calculations which might in the end prove to 

 have no real bearing on actual phenomena, owing to his own imperfect apprecia- 

 tion of the true atmospheric conditions. The meteorologist, on the other hand, 



' Ordered bv the General Committee to be printed in e-itenso. 



