12 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Jan., 1905. 



clear picture " is obtained " even witii two sheets of 

 gelatine. " When there are interposed " even as many 

 as six or more sheets, still the picture of the scratches 

 is distinct." " It is remarkable that such a vapour 

 should readily pass through media such as g-elatine, 

 celluloid, etc., and not by mere absorption, but in such 

 a way as to produce a picture of the surface from which 

 it emanated." " The remarkably clear pictures . 

 which can be produced through a sheet, or even several 

 sheets, of the thin gelatine, proves that the action is 

 not one of mere absorption." In his third paper on 

 the subject, read before the Royal Society, Dr. Russell 

 says, •• How then does the peroxide permeate the gela- 

 tine? Not by the ordinary process of diffusion, for 

 hydrc^en cannot diffuse through it, so that it must be 

 bv a process of dissolving, or very feebly combining 

 with the medium, or with a constituent of it, and, thus 

 travelling through, escape on the other side. That the 

 action is of this nature seems rendered probable by the 

 following experiments." These experiments consist in 

 placing a succession of plates, each for twenty min- 

 utes, over a solution of hydrogen peroxide covered with 

 a thin sheet of gelatine, and show that the active agent 

 apparently takes time to penetrate the gelatine. Tlie 

 first plate showed no result, the second a slight action, 

 the third still more, and so on. The same kind of 

 action takes place if zinc is used instead of hydrogen 

 peroxide, or celluloid instead of gelatine. 



Thus the production of a detailed image, although 

 several sheets of gelatine were interposed between the 

 active substance and the plate, was acknowledged by 

 Dr. Russell as ditlicuit to understand, and he says in 

 another place that it " seemed to prove that the action 

 was not a mere absorption on the one side and a giving 

 out on the other." The effect points to the obvious sug- 

 gestion that the effective agent is some form of radiant 

 energy. In 1898 I suggested that as all the active 

 substances experimented with in this connection were 

 susceptible of oxidation by mere exposure to air, and 

 as during their vigorous oxidation (combustion) a form 

 of radiant energy which will affect a photographic 

 plate was certainly produced, it might be that the slow 

 oxidation produced a similar form of radiant energy, 

 just as the total heat effect is supposed to be the same 

 whether the oxidation is slow or rapid. I pointed out the 

 relatively enormous exposures given in Dr. Russell's ex- 

 periments. One ten-thousandth of a second is cer- 

 tainly ample time to produce the developable condition 

 in the silver salt of a gelatine plate when it is exposed 

 to burning zinc, and it seems not unlikely that an 

 exposure of, say, six hours to the slowly oxidising 

 metal should produce a similar effect, for this increase 

 in the time of exposure is equal to the increase of from 

 one second to more than six-and-a-half years. 



There have been other opinions expressed, and 

 suggestions offered, with regard to the character of 

 the cause of these effects, and these I propose to refer 

 to next month. 



Zambcx cameras — flat film changing. — These cameras 

 now being introduced by Messrs. R. and J. Beck, are 

 distinguished by the novel and ingenious method of 

 changing the filmN. This operation is accomplished by 

 opening wide the solid hinged lid at the back of the 

 camera, so that the zambex envelope, which is rather 

 more than twice the length of the film, is opened out 

 flat and to its full length. A numbered tab, corre- 

 sponding to the exposed film, is then firmly drawn along 

 away from its position in front of the bundle until it 

 is in that part of the envelope that is attached to the 



lid. This leaves the next film ready for exposure, the 

 lid, of course, being first closed. The film carriers 

 are pieces of moderately- stiff black paper with pro- 

 jecting tabs to pull them by, and they arc attached to 

 one another by thinner paper that rolls over as each 

 is drawn along, and so prevents any friction against 

 the surface of the next film. If it is desired to focus, 

 the exposed films may be pushed back into their 

 original position, and the envelope with it-s whole 

 charge removed to make room for the screen. 

 On replacing the arrangement for the next ex- 

 posure the exposed films are drawn up again. When 

 ihe last is exposed, the film carriers are all pushed back, 

 and the envelope, with its contents in the same relative 

 positions as before use, is removed to make room for 

 a new one. The zambcx skeleton, or series of carriers, 

 in its envelope, may be obtained loaded with films, and 

 then all the changing operations are done in daylight; 

 they are also supplied empty, that the user may charge 

 them with any films preferred. The skeletons may be 

 used five times if desired, being provided w-ith five holes 

 to take a staple that retains all except the one that is 

 being removed from the front. Zambex skeletons are 

 also made to carry three plates instead of twelve films. 

 The advantages of this new device are obvious. Each 

 envelope with its full charge is less than half an inch 

 thick, so that the packages are compact as well as 

 light. 



The Piesmic Barometer. 



A new mercurial barometer, wliich lias been designed by 

 Mr. A. S. Davis, M.A., and has been called by him Ihe Piesmic 

 barometer, is an ingenious adaptation of an easily understood 

 principle in the relation between pressure and volume in gases ; 

 and presents as practical advantages several new features of 

 convenience, lightness, and trustworthiness. The action of 

 the instrument depends on the fact that any volume of air 

 taken at a low pressure, is more compressed than an equal 

 volume of air taken at a higher pressure, when the pressure 

 on each volume is increased by the same amount. The follow- 

 ing is a description of the method of the instrument, which is 

 of so convenient a size that it could, without very much in- 

 convenience, be carried in the inner pocket of an overcoat. 



ADC is a glass tube, the part AI> being made of strong 

 capillary tubing of one-tenth inch bore and liC being made of 

 thin rjuill tubing. A U is seven inches long, and the capacity 

 of the whole tube is 35 times the capacity 

 of a single inch of the capillary tubing. The 

 end /) , opens into a small cast-iron cistern 

 E containing mercury. The air in this 

 cistern, though not in actu.il conmiunication 

 with the external air, is kept at atmospheric 

 pressure by communication with a small 

 auxiliary chanibtT, the sides of which are of 

 thin paraffnied paper. When the tube is 

 horizontal the mercury lies on one side of 

 the cistern, leaving the open end A of the 

 tube exposed to the air. When the tube is 

 brought into a verticil position the mercury 

 flows over and closes the mouth of the tube, 

 then flows down the tube to .1 greater or less 

 depth, the depth being dependent upon 

 the atmospheric pressure at the time. If 

 the barometer is standing at 30 inches the 

 mercury will descend five inches; if at 29 

 inches it will descend six inches : if at 2H 

 inches, seven inches, and so on. A scale of 

 inches being placed behind the tube, the reading of the end of 

 the mercury column against this scale shows the height of the 

 barometer at the time. 



