304 



NATURE 



\yan. 27, 1 88 1 



seen is simply this, that if au analyser is arranged to stop the light 

 and make the field quite dark before the magnet is excited, then 

 directly the battery is connected and the magnet called into action 

 a faint and barely perceptible brightening of the field occurs ; 

 which will disappear if the analyser be slightly rotated. [The 

 experiment was then shown.] Now no wonder that no one 

 understood this result. Faraday himself did not understand it at 

 all ; he seems to have thought that the magnetic lines of force 

 were rendered luminou^■, or that the light was magnetised ; in 

 fact he was in a fog, and had no idea of its real significance. 

 Nor had anyone. Continental philosoi hers experienced some 

 difficulty and several failures before tlicy w ere able to repeat the 

 experiment. It was in fact discovered too soon, and before the 

 scientific world was ready to receive it, and it was reserved for 

 Sir William Thomson briefly, but very clearly, to point cut, 

 and for Clerk Maxwell more fully to develop, its most important 

 consequences. [The principle of the experiment was then 

 illustrated by the aid of a mechanical model.] 



This is the fundamental experiment on which Clerk Maxwell's 

 theory of light is bated ; but of late years many fresh facts and 

 relations between electricity and light have been discovered, and 

 at the present time they are tumbling in in great numbers. 



It was found by Faraday that many other trans-parent media 

 besides heavy glass would show the phenomenon if plactd 

 between the poles, only in a less degree ; and the very impoitant 

 observation that air itself exhibits the same phenomenon, though 

 to an exceedingly small extent, has just been madebyKundt and 

 Rontgen in Germany. 



Dr. Ken-of Glasgow has extended the result toopaque bodies, and 

 has shown that if light be passed through magnetised ;>o« its plane 

 is rotated. The film of iron must be exceedingly thin, because of 

 its opacity, and hence, though the intrinsic rotating power of 

 iron is undoubtedly very great, the observed rotation is exceed- 

 ingly small and difficult to observe ; and it is only by very 

 remarkable patience and care and ingenuity ihat Dr. Kerr has 

 obtained his result. Mr. Fitzgerald of Dublin has examined 

 the question mathematic.nlly, and has shown that Maxwell's 

 theory would have enabled Dr. Kerr's lesult to be predicted. 



Another requireaient of the theory is that Vodies which are 

 transparent to light must be insulators or non-conductors of 

 electricity, and that conductors of electricity are necessarily 

 opaque to light. Simple observation amply confirms this ; 

 metals are the be-t conductors, and are the most opaque b^sdies 

 known. Insulators such as glass and crystals are transparent 

 whenever they are sufficiently homogeneous, and the very 

 remarkable reseaixhes of Prof. Graham Bell in the last few 

 months have shown that even ebonite, one of the most opaque 

 insulators to ordinary vision, is certainly transparent to some 

 kinds of radiation, and transparent to no small degree. 



[The reason \\\\y transparent bodies must insulate, and why 

 conductors must be opaque, was here illustrated by mechanical 

 models.] 



A further consequence of the theory is that the velocitv of 

 light in a transpa-ent medium will be affected by its electrical 

 strain con^tant ; in other \\ords, that its refractive index will 

 bear some close but not yet quite ascertained relation to its 

 ■ specific inductive capacity. Experiment has partially confirmed 

 this, but the confirmsition is as yet very incomplete. Hut there 

 are a number of results not predicted by theory, and whose con- 

 nection with the theory is not clearly made out. We have the 

 fact that light falling on the platinum ebctrode of a voltameter 

 generates a current, first observed, I think, by Sir W. R. Gr.:,ve 



at any rate it is mentioned in his " Correlation of Forces ' — 

 extended by Recquerel and Robert Sabine to other substances, 

 and now being extended to fluorescent and other bodies by Prof. 

 Minchin. And finally — for I must be brief — we have the rem.ark- 

 able action of light on selenium. This fact was discovered 

 accidentally by an a.ssistant in the laboratory of Mr. Willoughby 

 Smith, who noticed that a piece of selenium conducted elec- 

 tricity very much better when light was falling upon it than 

 when it was in the dark. The light of a candle is sufficient, and 

 instantaneously brings down the resistance to something hke 

 one-fifth of its original value. 



I could show you these effects, but there is not much to see ; it 

 is an intensely interesting phenomenon, but its external manife,- 

 tation is not striking — any more than Faraday's heavy glass 

 experiment was. 



This is the phenomenon which, as you know, has been utilised 

 by Prof. Graham Bell in that most ingenious and striking inven- 

 tion, the photophone. By the kiirdness of Prof. Silvanus 



Thompscn I have a few slides to show the principle of the 

 invention, and .Mr. Shelford Bidwell has been good enough to 

 lend me his home-made photophone, which answers exceedir^ly 

 well for short d'stances. 



I have now trespassed long enough upon yom- patience, bat I 

 mu'-t just allude to what may very likely be the next striking 

 popular discovery, and that is the transmission of light by elec- 

 tricity ; I mean the transmission of such things as views and 

 pictures by means of the electric wire. It has not yet been 

 done, but it seems already theoretically possible, and it may 

 very soon be practically accomplished. 



ENDOWMENT OF RESEARCH IN 

 BIRMINGHAM 

 "TrilE President of the Birmingham Philosophical Society, 

 Dr. Heslop, recently gave an address to the members, 

 taking for his su'ject the "Scientific Situation in Birmingham." 

 Having reviewed the various local agencies set up during the 

 past year for the diffusion of knowledge, including the op.ening 

 of Mason's Science College, he went on to say : I must now 

 allude to the most important work undertaken by the Society, 

 the establishment of the fund for the endowment of research. 

 This action has received warm support in many quarters, and 

 has in fact done more to place it in a favourable light before 

 the country than any privious circumstances. Although the 

 elforts made to rai-e this fund have been inconsiderable, jet 

 nearly loc/. in annual subscriptions, of varying dates, and 900/. 

 in donations have been obtained. The Council have invested 

 600/. in order to ensure the permanence of the fund. It is 

 ps-oballe that some slight additions may be made to this sum, 

 having the same object in view ; but it is, I believe, their inten- 

 tion to recommend the Society to spend the whole income, how. 

 soever derived, in annual grants to persons living in this town 

 or neighbourhood who devote themselves wholly or in part to 

 science research. It is an error to suppose that this fund is to 

 be allotted either to any particular individual or specially t > 

 members of this Society. The Council are free to do what they 

 deem best with the money intrusted to them, viilhin the limits 

 of the scheme agreed upon. There is another temporary limit 

 to their powers. One eminent investigator (Dr. Gore) is allotted 

 a certain sum for a certain period. The approval of this step 

 evinced by those who have contributed to the fund, and by 

 others, has been a source of satisfaction to the Council. 



I wish now to remind you that the scheme in connection with 

 this subject declares that "the Council are of opinion that this 

 Society would be omitting a principal means of the advancement 

 of science — the end for which all such associations exist — if it 

 neglected the question of the endowment of research. To main- 

 tain a successful investigator in his labours, even though no 

 results of immediate or obvious utility can be shown to spring 

 out of them, is of interest to the community at large." It may 

 be that yiu will pronounce these words to be truisms scarcely 

 requiring formal enunciation. The fact is that though the sense 

 of them has been repeatedly given to the public in late years, 

 practical action has not ensued. Everybody is telling his neigh- 

 bour what a good thing it would be if men endowed with an 

 aptitude for research into the facts of nature were also endow ed 

 with the means of living during their work. The speaker and 

 the listener go by on the other side, and no good Samaritan 

 tenders help to the well-praised searcher after truth. Nay, Mr. 

 Mark Fattison affirms in his late bcok on Milton that "the 

 England of our day has decided against the endowment of 

 science," and seems lo think that the principle on which the 

 decision is based may be wrong, but "is not unreasonable." 

 But the endowment of ministers of science stands on quite anot'cer 

 foundation from that of ministers of religion. "To assign a 

 place with a salary," says Mr. Pattison, " is to offer a pecuniary 

 inducement to simulate" the qualification, i.e. a state of grace. 

 But in the ca^e of science there is no question of place, and the 

 endowment is offered, not to those who promise much, but to 

 those who have already performed something ; not to those who 

 imagine themselves to be in the requisite spiritual state, but to 

 those who, working for an audience, select though few, have 

 demonstrated that they are touched by the divine fire which 

 burns not for other men. 



In the opinion of others the only piratticable mode of dealing 

 with this question is by bestowing adequate funds on teachers, 

 and by placing them in favourable conditions for research. 



