Jan. 18,1872] 



NATURE 



2\\ 



In the event of nitrate of silver being used for preparing 

 the paper, it is necessary, obviously, to exclude the light, 

 as otherwise a reducing action will be already set up by 

 solar means alone, but with the salts of palladium or 

 platinum no such action need be feared. According to 

 the kind of metallic salt employed, so the tint ol the 

 impression vanes, but in most c.ises an intense black may 

 be obtained where the action has proceeded far enough. 



Having described M. Merget's discoveries thus far, it is 

 easy to guess how that gentleman employs them in the 

 carrying out of a photographic process. An ordinary 

 glass negative, possessing an image which has been formed 

 by the deposition of silver particles, is prepared in a suit- 

 able manner to protect it from injury by contact with the 

 mercury (such, for instance, as coaling it in some way 

 with platinum or carb >n particles), and the picture is then 

 exposed to the action of mercury vapour. The vapour 

 condenses, in a more or less concentrated form, upon the 

 image — in the same way, pretty well, as it becomes de- 

 posited upon, and develops, the latent miagc in the 

 daguerreotype process— and substquently the plate thus 

 treated is brought into contact with the sensitive paper. 

 The consequence is that the minute particle-3 of mercury 

 depo:ited all over the image exercise a reducing action 

 upon the salis on the surface ( f the paper, and a print 

 results of the original plioto^jraph, poss-ssing the same 

 gradation of tint as the original. Indeed, when nitrate 

 of silver is employed for sensitising the paper, the photo- 

 graph secured is in every respect simdar to that produced 

 by light in the ordinary silver printing process, and the 

 picture is forthwith toned and fixed in the same way, 

 in fact, as one of these ; in the one case, however, the 

 redaction of the silver salts has been brought about by 

 mercury vapour, while in the other light alone has 

 been the reducing agent. Iniijressions obtained by means 

 of platinum and palladium salts need simply to be washed 

 in water in order that they may be permanently fixed. 

 These latter, in truth, are so indestructible and inalterable 

 that they cannot be destro\ed except by a chemical 

 agent which would at the same time radically injure the 

 paper, or other basis, upon which they rest. 



This process of photography is not yet in such an ad- 

 vanced state as to be of any practical importance ; but, 

 nevertheless, it is certainly one of the most ingenious and 

 interesting discoveries made of late in this branch of 

 Science. The great advantage it possesses is that of 

 printing without the aid of light, and yet producing prints 

 with detail and half-tone dependent upon delicate chemical 

 reaction— such rare gradation being secured as our pre- 

 sent light printed pictures (silver and carbon prints) alone 

 possess. A mechanical printing process could, of course, 

 easily be worked out from these data, if considered desir- 

 able ; and, indeed, it is by no means improbable that this 

 will be thi' most successful way of applymg the discoveries 

 in a practical form. But even in the event of no practical 

 use at all being made of the process— (or this is indeed 

 questionable — the research, regarded from a purely scien- 

 tilrc point of view, is deserving 01 the highest eulogium. 

 H. Baden Pritchard 



NOTES 



In another column will be found full details of the observa- 

 tions of the Total Eclipse of December 12, made at Bekul, by 

 Mr. Norman Lockjer and Captain iMaclear. In future numbers 

 we hope to give similar reports from the observers at the other 

 stations. The weather was very favourable at all the stations, 

 with only one exception. 



M. Janssen writes as follows to the French Academy of 

 Sciences, under date Sholoor, Neelgherry, 12th of December, 

 1871, 10 A.M. : — "I have just observed the eclipse, only a few 

 moments since, with an admirable sky, and whilst still under the 



emotion caused by the splendid phenomenon of which I have 

 just been a witness, I address a few lines to you by the Bomb.iy 

 courier, who is to start instantly. The result of my observations 

 at Sholoor indicates without any doubt the solar origin of the 

 corona, and the existence of matter beyond the chromosphere." 

 And in a letter to M. Faye, written half an hour later, he says :— 

 " I have ju>t seen the corona, as it was impossible for me to do 

 in 1868, when I was entirely occupied with the speclnim of the 

 protuberances. Nothing can be finer, nothing more luminou-, 

 with peculiar forms which exclude all possibility of a terrestrial 

 atmospheric origin. The spectrum contains a very remarkable 

 brUliant green line already indicated ; it is not continuous, as has 

 been asserted, and I have found in it indications of the obscure 

 lines of the solar spectrum (especially D). I believe the question 

 whether the corona is due to the terrestrial atmosphere is 

 settled, and we have before us the prospect of the study of the 

 extra-solar regions, which will be very interesting and fertile." 



PkOF. Hu.xlEy's friends, and the scientific world generally, 

 will learn with great regret that he has been compelled to re- 

 linquish all work for the present, his medical advisers havinrr 

 ordered him complete rest for two months, for which purpose he 

 has just started fur Egypt. There is every prospect that at the end 

 of the time he will return to his old work with renewed vigour. 



The Regius Pro.fesorship of Physic in the University of Cam- 

 bridge has bicome vacant by the redgnation of D.-. Bond, who 

 has held the office since 1851. 



The Council of the College of Preceptors has arranged fur 

 the delivery of a series of three lectures to the members of t'le 

 college and their friends, on the teachiig of science in secondary 

 schools. The first lecture of the senes, " On Teaching Phy- 

 sics," was delivered at the rooms of the College, 42, Queen 

 Square, on Saturday evening, the 13th instant, by Professor 

 G. C. Foster, F. R. S. ; the second, " On Teaching Me- 

 chanics," was delivered yesterday (Wednesday) evening by Prof. 

 W. C Adams ; and the thirJ, " On Teaching Botany and 

 Geology," is to be delivered on Monday evening, 22nd inst., 

 by Mr. J. M. Wilson, of Rugby. The point mainly insisted on 

 by Prof. Foster in his lecture, was the necessity, in order to 

 make the study of Physics of much use as a training for the 

 mind, that the pupils should not only see, but actually make ex- 

 periments for themselves, so that the principal f.icts and pheno- 

 mena discussed may be known to them as matters within their 

 own experience. 



A SEKIES of lectures will be delivered in Gresham Col- 

 lege, Basinghall Street, by Mr. E. Symes Thompson, M.D., 

 F.K.C. P. , .as follows: — Thursday, January iS, 1S72, On the 

 Digestive Organs in Health and Disease (continued from last 

 course) ; Friday, January 19, 1872, On the Blood Vessels ; Saiur- 

 day, January 20, 1872, On the Pulse. 



At the first Anniversary Meeting of the Anthropological Insti- 

 tute, held January 15, Sir John Lubbock, Bart., M.P., F.R.S., 

 president, in the chair, the president delivered an address, and 

 the officers and councils to serve fir 1S72 were elected as 

 follows :— President — Sir John Lubbock, Bart., M.P., F.R.S. ; 

 Vice-Presidents— Mr. W. Blackmore, Prof Busk, F. R.S., Dr. 

 Charnock, Mr. John Evans, F.R.S., Mr. George Harris, Prof. 

 Huxley, F.R.S. ; Director — Mr. E. W. Brabrook ; Treasurer — 

 Mr. J. W. Flower ; Council— Mr. H. C. Bohn, Captain K. F. 

 Burton, Mr. James Butler, Mr. A. Campbell, M.D., F.R.S., 

 Mr. Hyde Clarke, Mr. J. Barnard Davis, M.D., -Mr. Robert 

 Dunn, Mr. David Forbes, F.RS., Colonel A. Lane Fox, 

 Mr. A. W. Franks, Sir Duncan Gibb, Bart., M.D., Mr. Joseph 

 Kaines, Mr. Richard King, M.D., Mr. A. L. Lewis, Mr. 

 Clements R. Markham, Captain Bedford Pim, R.N., Mr. F. G. 

 Price, Mr. C. Robert dej Ruffieres, Mr. Spottiswoode, V.P.R.S., 

 Mr. C. Staniland Wake. 



