400 



NATURE 



[August 24, 1882 



tesimal periods of time gas may itself be as rigid and as brittle 

 as glass. 



5. That stria: are not merely loci in which electrical is converted 

 into luminous energy, but are actual aggregations of matter. 



This last conclusion was based mainly upon experiments made 

 with an induction coil excited in a new way — viz. directly by an 

 alternating machine, without the intervention of a commutator 

 or condenser. This mode of excitement promises to be one of 

 gTeat importance in spectroscopic work, as well as in the study 

 of the discharge in a magnetic field, partly on account of the 

 simplification w hich it permits in the construction of induction 

 coils, but mainly on account of the very great increase of strenglh 

 in the secondary currents to which it gives rise. 



These investigations assume additional importance when v\e 

 view them in connection with solar — I may even say stellar — 

 physics, for evidence is augmenting in favour of the view that 

 interstellar space is not empty, but is filled with highly attenuated 

 matter of a nature such as may be put into our vacuum tubes. 

 Nor can the matter occupying stellar space be said any longer to 

 be beyond our reach for chemical and physical test The spec- 

 troscope has already thrown a flood of light upon the chemical 

 constitution and physical condition of the sun, the stars, the 

 comets, and the far distant nebulae, which have yielded spectro- 

 scopic photographs under the skilful management of Dr. 

 Huggins, and Dr. Draper of New York. Armed with greatly 

 improved apparatus, the physical astronomer has been able to 

 reap a rich harvest of scientific information during the short 

 periods of the last two solar eclipses — that of 1879, visible in 

 America, and that of May last, observed in Egypt by Lockyer, 

 Schuster, and hy Continental observers of high standing. The 

 result of this last eclipse expedition has been summed up as 

 follows: — "Different temperature levels have been discovered 

 in the solar atmosphere ; the constitution of the corona has 

 now the possibility of being determined, and it is proved to 

 shine with its own light. A suspicion has been aroused once 

 more as to the existence of a lunar atmosphere, and the position 

 of an important line has been discovered. Hydro-carbons do 

 not exist close to the sun, but may In space between us and it." 



To me personally these reported results possess peculiar inte- 

 rest, for in March last I ventured to bring before the Royal 

 Society a speculation regarding the conservation of solar energy, 

 which was based U| on the three following postulates, viz. : — 



1. That aqueous vapour and carbon compounds are present in 

 s ellar or interplanetary space. 



2. That these gaseous compounds are capable of being disso- 

 ciated by radiant solar energy while in a state of extreme 

 attenuation. 



3. That the effect of solar rotation is to draw in dissociated 

 vapours upon the polar surfaces, and to eject them after com- 

 bustion has taken place back into space eqnatorially. 



It is therefore a matter of peculiar gratification to me that the 

 results of observation here recorded give considerable support to 

 that speculation. The luminous equatorial extensions of the sun 

 which the American observations revealed in such a striking 

 manner (with which I was not acquainted when writing my 

 paper) were absent in Egypt ; but the outflowing equatorial 

 streams 1 suppose to exist could only be rendered visible by re- 

 flected sunlight, when mixed with dust produced by exceptional 

 solar disturbances or by electric discharge ; and the occasional 

 appearance of such luminous extensions would serve only to dis- 

 prove the hypothesis entertained by some, that they are divided 

 planetary matter, in which case their appearance should be per- 

 manent. Prof. Langley, of Pittsburg, has shown, by means of 

 his bolometer, that the solar actinic rays are absorbed chiefly in 

 the solar instead of in the terrestrial atmosphere, and Capt. 

 Abney has found by his new photometric method that absorp- 

 tion due to hydrocarbons takes place somewhere between the 

 solar and terrestrial atmosphere ; in order to test this interesting 

 result still further, he has lately taken his apparatus to the top of 

 the Kiffel with a view of dimiui hing the amount of terrestrial 

 atmospheric air between it and the sun, and intends to bring a 

 paper on this subject before Section A. Stellar space filled with 

 such matter as hydrocarbon and aqueous vapour would establish 

 a material continuity between the sun and his planets, and 

 between the innumerable solar systems of which the universe is 

 composed. If chemical action and reaction can further be 

 admitted, we may be able to trace certain conditions of thermal 

 dependence and maintenance, in which we may recognise prin- 

 ciples of high perfection, applicable also to comparatively 

 humble purposes of human life. 



We shall thus find that in the great workshop of nature there 

 are no lines of demarcation to be drawn between the most exalted 

 speculation and common-place practice, and that all knowledge 

 must lead up to one great result, that of an intelligent recogni- 

 tion of the Creator through His works. So then, we members 

 of the British Association and fellow workers in every branch of 

 science may exhort one another in the words of the American 

 bard who has so lately departed from amongst us : — 

 *' Let us then be up and doing, 

 Wilh a heart for any fate ; 

 Still achieving, still pursuing, 

 Learn to labour and to wail." 



SECTION A 



mathematical and physical 



Opening Address by the Right Hon. Lord Raylkigh, 



M.A., F.R.S., F.K.A.S, President of the Section 



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

 recognise that probably the most useful form which a presidential 

 address could take, would be a summary of the progress of 

 ph\sics, or of some important branch of physic-, during recent 

 years. But the difficulties of such a task are considerable, and 

 I do not feel myself equal to grappling w ith them. The few 

 remarks which 1 have to offer are of a general, I fear it may 

 lie 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 

 this 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 

 our section is unintelligible to an< ther, and that details whore 

 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 difficulty 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, there is room, and indeed necessity, 

 for great variety of treatment. One class of investigators relies 

 mainly upon reiterated appeals to experiment to resolve the 

 questions which appear still to be open, while another prefers, 

 with Thomas \ oung, 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, w e cannot afford to neglect the confir- 

 mations which our view's may derive from the companion of 

 mea-urements made in different fields and in face of different 

 experimental difficulties. Examples of the inter-dependence of 

 measurements apparently distinct will occur to every physicist. 

 I may mention the absolute determinations of electrical resis 

 tance, 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 be properly be 

 satisfied for a time with work of a le -s severe and accurate 

 character, knowing that with the progress of knowledge the 

 way is sure to be smoothed. both by a better appreciation of the 

 difficulties involved, and by the invention of improved experi- 

 mental appliances. I hope I shall not be misunderstood as 

 underrating the importance of great accuracy in its proper place 

 if I express the opinion that the desire for it has sometimes had 

 a prejudicial effect. In cases where a rough result would have 

 sufficed for all immediate purposes, no measurement at all has 

 been attempted, because the circumstances rendered it unlikely 

 that a high standard of precision could be attained. Whether 

 our aim be more or less ambitious, it is important to recognise 



