May 2, 1898. 



KNOWLEDGE. 



115 



Scattered through the pages of the photographic journals 

 are many reports of single observartions, and short series of 

 experiments on similar lines to those of l>r. Russell, and 

 the results have been variously ascribed to heat, to X rays, 

 to magnetism, to " dark light," etc. ; but it seems to have 

 been left to Dr. Russell to carry out a comprehensive series 

 of experiments, and to — in some measure — raise the veil 

 ■which has hitherto shrouded these phenomena in obscurity. 

 i)r. Russell found, incidentally, and in the course of 

 experiments for another purpose, that zinc, if placed in 

 contact with a photographic dry plate, had some action 

 upon it which would enable it to be developed as if it had 

 been exposed to light ; and, further, that a similar action 

 was exerted by many other metals, by wood, by straw- 

 board, by many printed papers (which would leave a clear 

 impression of their printed matter), etc., etc. All these 

 results he detailed in a paper before the Royal Society 

 about a year ago ; and in the meanwhile he has been 

 repeating.verifymg, and extendinghis observations, with the 

 results which were brought forward in the recent Bakerian 

 Lecture. At first the zmc and other materials were placed 

 in contact with the photographic plates, and it was found 

 that after a week's contact an image could be developed 

 which would plainly show such minute marks as scratches 

 on the zinc ; that the structure, rings of growth, etc., in a 

 section of a pine tree, and even the grain of mahogany 

 which had formed part of a piece of furniture, and had 

 been practically in darkness for a couple of centuries or 

 more, were also plainly visible ; and that not only the 

 printing, but also the water-marks and accidental defects 

 on certain papers, could be developed on the plates. When 

 the objects were placed at a little distance from the dry 

 plate (gradually increased to an inch or more) the efifect 

 was still produced, but, of course, without any detaQ being 

 visible. Not only would the action thus pass through 

 an inch or more of air, but it also passed easUy through 

 gelatine, celluloid, collodion, and gutta-percha tissue. 

 Glass was found to be quite impervious, though, curiously 

 enough, glass was pervious to the emanation from some 

 of the uranium salts which were tested, and which acted 

 very strongly, whether in the dry state or in solution. 

 This point is important, since it shows that there are at 

 least two classes of emanation ; and other experiments 

 point to the possibility of there being several more. 



Amongst the most active metals are zinc, magnesium, 

 aluminium, nickel, lead, and bismuth. Cobalt, tin, and 

 antimony are less active, while copper and iron are prac- 

 tically inert. Strawboard and fresh charcoal act very 

 strongly upon the plate, as does copal varnish, even when 

 quite dry and hard. In the earlier experiments mercury 

 seemed to be one of the most energetic agents, but it had 

 since been shown that pure mercury was inactive, and that 

 the effects observed were due to zinc and lead contained as 

 impurities. 



With zinc, which is one of the most satisfactory subjects 

 for experiment, it is found that the action is strongest when 

 the face has recently been brightened (as by cleaning with 

 emery paper), and that old zinc, which is considerably 

 oxidized, has practically no effect upon the plate. 



The possibility of the action being due to what may be 

 called latent light was suggested, but Dr. Russell finds that 

 the action is the same whether the active substance has 

 been recently insulated or has long been k«pt in complete 

 darkness. 



The action of temperature is very important, and while 

 the necessary exposure for a good impression is usually 

 about a week (at a temperature of fifteen degrees Centi- 

 grade), an increase of temperature to fifty-five degrees will 

 reduce the exposure to a few hours. 



As to the cause of these results Dr. Russell does not 

 speak with certainty, but he has made many experiments 

 which confirm his idea that the effects are due to vapours 

 given off by the objects. On this point a great deal of 

 additional work is needed, especially in view of the signifi- 

 cant facts that the most volatile metals are not the most 

 active ; that some oils and gums (such as turpentine 

 and copal) will act strongly, while volatile substances 

 like alcohol and ether have no effect ; that the uranium 

 salts act strongly through glass ; and that a book printed 

 so long ago as IGll still gives a faint impression, while one 

 dated 1805 gives a strong impression on the plate. If the 

 results are due to a vapour it will be interesting to know the 

 conditions under which it can continue to be given off 

 through two hundred and fifty years. 



Altogether the field of research is most attractive and 

 promising, and the publication of Dr. Russell's results 

 should lead very many investigators to take it up. If they 

 do, I trust we may have more careful observation and less 

 hasty publication than was revealed by many of the 

 announcements made soon after the publication of the 

 work of Prof. Rontgen. 



BOTANICAL STUDIES.-III. 



JUNGERMANNIA. 



By A. Vaugha>- Jennings, f.l.s., f.g.s. 



OUR last study* dealt with a type of fruit formation 

 which is about the most highly developed among 

 the lower cellular plants. In ColeochcEte, whUe 

 the vegetative part of the plant consisted of a 

 simple cell-plate, it was noted that the reproductive 

 process was far more specialized than that in the first type, 

 ra!(c/(e''-(''/.t It was observed that the egg-cell (or ompher,) 

 after fertilization became surrounded by a layer of cells 

 developed from adjacent tissues, and also that it subse- 

 quently divided into a number of separate bodies (carpo- 

 sporrs), each of which could give rise to a new plant Uke the 

 parent. 



It is evident that both these modifications of the method 

 of reproduction are of great advantage to the chances of 

 survival of the plant. Not only is the egg-cell more 

 protected in its resting stage, but by dividing into several 

 independently living portions the probabihties of preserva- 

 tion of the type become vastly increased. Those genera in 

 which the liberated carpospores have the greatest activity 

 and the best power of resistance are those which will 

 survive and multiply. 



In the algie, and certain fungi which are probably their 

 degenerate descendants, this seems to be the highest stage 

 reached in the evolution of " fruits " and the phenomenon 

 of •' alteration of iienenitiom." When we look for the next 

 step there is a great break in the series, and one which we 

 shall probably never be able to bridge over satisfactorily. 

 There seems every reason to suppose that the early stages 

 in the evolution of the higher plants resulted from the 

 spreading of simple aquatic forms on to the land, their 

 attempt to gain a footing there, and to adapt themselves 

 to terrestrial conditions. 



What the intermediate stages were there is no evidence 

 to show. Delicate cellular plants have practically no 

 chance of preservation in the rocks of the earth's crust, 

 and geological science can give no help. The only avail- 

 able method of Investigation is the study and comparison 

 of living forms : their life history, and early stages of 

 development. 



* Knowledge, iJarch, 1S98. t Knowledge, January, 1898. 



