43: 



TRANSACTIONS OF THE SECTIONS. 



Section A.— MATHEMATICAL AND PHYSICAL SCIENCE. 



President op the Section — 

 The Eight Hon. Professor Lord Kayleigh, M.A., F.E.S., F.E.A.S., F.E.G.S. 



I 



THUBSBA r, A UG UST 24 . 



The President delivered the following Address : — 



In common with some of my predecessors in this chair, I recognise that probably 

 the most useful form which a presidential address coidd take, would be a summary 

 of the progress of physics, or of some important branch of physics, during recent years. 

 But the difficulties of such a task are considerable, and 1 do not feel myself equal 

 to grappling with them. The few remarks which I have to offer are of a general, 

 I fear it may be thought of a commonplace, character. All I can hope is that they 

 may have the effect of leading us into a frame of mind suitable for the work that 

 lies before us. 



The diversity of the subjects which come under our notice in thic section, as 

 well as of the methods by which alone they can be adequately dealt with, although 

 a sign of the importance of our work, is a source of considerable difficulty in the 

 conduct of it. From the almost inevitable specialisation of modern science, it has 

 come about that much that is familiar to one member of cur Section is unintelligible 

 to another, and that details whose importance is obvious to the one fail altogether 

 to rouse any interest in the mind of the other. I must appeal to the authors of 

 papers to bear this difficult}' in mind, and to confine within moderate limits their 

 discussion of points of less general interest. 



Even within the limits of those departments whose foundation is evidently 

 experimental, tliere is room, and indeed necessity, for great variety of treat- 

 ment. One class of investigators relies mainly upon reiterated appeals to experi- 

 ment to resolve the questions which appear still to be open ; while another prefers, 

 with Thomas Young, to base its decisions as far as possible upon deductions from 

 experiments already made by others. It is scarcely necessary to say that in the 

 present state of science both methods are indispensable. Even where we may fairly 

 suppose that the fundamental principles are well-established, careful and often 

 troublesome work is necessary to determine with accuracy the constants which 

 enter into the expression of natural laws. In many cases the accuracy desirable, 

 even from a practical point of view, is hard to attain. In many others, where the 

 interest is mainly theoretical, we cannot afford to neglect the confirmations which 

 our views may derive from the comparison of measurements made in different fields 

 and in face of different experimental difficulties. Examples of the inter-depen- 

 dence of measurements apparently distinct will occur to every physicist. I may 

 mention the absolute detei'minations of electrical resistance, and of the amounts of 

 heat developed from electrical and mechanical work, any two of which involve also 

 the third, and the relation of the velocity of sound to the mechanical and thermal 

 properties of air. 



Where a measurement is isolated, and not likely to lead to the solution of any 

 open question, it is doubtless possible to spend upon it time and attention that 

 might with advantage be otherwise bestowed. In such a case we may properly be 



