TRANSACTIONS OF SECTIGIf A. 549 



Independently of all this, Herr Otto Wiener, imitating Hertz's experiments 

 with ordinary light, in 1889 reflected a beam directly back on itself, and, by inter- 

 posing a very thin collodion iilm at extraordinarily oblique incidence, succeeded in 

 the difficult experiment of so magnifj^ng by the cos^ine of inclination the half 

 wave-length, as to get the silver deposited iu strata of visible width, and thus to 

 photograph the interference nodes themselves at the places where they were cut by 

 the plane of the film.^ 



Then M. Lippmann, using a thicker film, not put obliquely but normal to the 

 light, obtained the strata within the thickness of the film itself— hundreds of 

 layers ; and so, employing incidence light of definite wave-length, was able to pro- 

 duce a stratified depo&it, which reflected back at appropriate incidence the same 

 wave-length as produced it ; thus reproducing, of course, the definite colour. 



It is probable that the silver is first shaken out at the ventral segments, but 

 that the strata so formed are thick and blurry. I conjecture that by over-exposure 

 this deposit is nearly all mopped up again, traces being left only at the nodes, 

 where the action is very feeble and takes a long time to occur ; "but that these 

 residual strata, being fairly sharp and definite, would be likely to give much better 

 effects. And so I suppose that these are what are actually effective in obtaining 

 M. Lippmann's very interesting, though not yet practically useful, result. 



_ I now leave the retrospect of what has been done, although many other topics 

 might usefully detain us, and I proceed to glance forward at the progres.% ahead 

 and at the means we have for efl'ectively grappling with our due share of it. 



_ There is a subject which has long been in my mind, and which I determined to 

 bring forward whenever I had a cathedral opportunity of doing so ; and now, if 

 ever, is a suitable occasion. It is to call attention to the fact that the further 

 progress of physical science in the somewhat haphazard and amateur fashion in 

 which it has been hitherto pursued in this country is becoming increasingly difficult, 

 and that the quantitative portion especially should be undertaken in a permanent 

 and publicly-supported physical laboratory on a large scale. If such an establish- 

 ment were likely to weaken the sinews of private enterprise and individual research 

 it should be strenuously opposed; but, in my opinion, it would have the opposite 

 effect, by relieving the private worker of much which he can only undertake with 

 great difficulty, sacrifice, and expense. To illustrate more precisely what I 

 mean, it is sufficient to recall the ease of astronomy. The amateur astronomer has 

 much work lying ready to his hand, and he grapples with it manfully. To him is 

 left the striking out of new lines and the guerilla warfare of science. Skirmishing 

 and brilliant cavalry evolutions are his natural field : he should not be called upon 

 to take part in the general infantry advance. It is wasting his energies, and he 

 could not in the long run do it well. What, for instance, would have been the 

 state of astronometry — the nautical almanac department of astronomy — without 

 the consecutive and systematic work of the National Observatory at Greenwich H 

 It may be that some enthusiastic amateurs would have devoted their hves to this 

 routine kind of work, and here at one time and there at another a series of accurate 

 observations would have been kept for several years. Pursued in that way, how- 

 ever, not only would the effort be spasmodic and temporarv, but the energy and 

 enthu-siasm of those amateurs would have been diverted from the pioneering more 

 suited to them, and would have been cramped in the e-roove of routine, eminently 

 adapted to a permanent official staff" but not wholesom^e for an individual. 



Long-continued consecutive observations may be made by a leader of science, 

 as functions may be tabulated by an eminent mathematician ; but if the work can 

 be done almost equally well (some would say better) by a professional observer or 

 pomputator, how great an economy results. 



Now all this applies equally to physics. The ohm has been determined 

 with 4-figure, perhaps with 5-figure, accuracy ; but think of the list of eminent 

 men to whose cevere personal labour we owe this result, and ask if the spoil is worth 

 the cost. Perhaps in this case it is, as a specimen of a well-conducted determina- 

 tion, "^e must have a few specimens, and our leaders must show us the way to do 

 things. But let us not contmue to use them for such purposes much longer. The 



' WJPifemann's Annalen, vol. xl. 1890. 



