326 



KNOWLEDGE. 



September, 1913. 



two lightest known gases — which are driven away 

 from the Earth in the direction opposite to the Sun ; 

 but the absence of sensible parallax is a serious 

 objection here also, unless we suppose that these 

 particles are already far beyond the Moon when 

 they are observed. Gylden, the Swedish mathe- 

 matical astronomer, has shown that meteors passing 

 near opposition in the neighbourhood of the Earth 

 could follow one or other of several oscillating orbits 

 round the point of opposition before resuming their 

 course around the Earth or Sun. Even if these 

 minute particles were very numerous they would not 

 exercise any appreciable attraction upon one another 

 or much influence on the Earth, but still they would 

 present the appearance of a kind of luminous fog in 

 opposition to the Sun. The centre of this luminous 

 path would be the point in the sky directly opposite 

 the Sun : its outline elliptical and its major axis lying 

 along the Ecliptic. Since the observed deviation 

 from perfect circularity is but small, it must be con- 

 cluded that the meteors move round the Earth in all 

 directions, without there being many more in the 

 ecliptic plane than in any other. 



Mr. Innes has proposed a modification of an 

 earlier theory to account for the Gegenschein. He 

 considers that the Earth is continually bombarded by 

 meteorites which give off " corpuscles." These 

 latter, repelled by the Sun and Earth together, 

 produce a kind of feeble tail, smaller than that of a 

 comet, which is visible on a dark night in the part 

 of the sky just opposite the Sun. 



Although, as we have seen from the various 

 accounts and views just given, there is still con- 



siderable divergence of opinion as to its true nature, 

 and much still remains for observation, especially in 

 regions more favoured than our own, yet we may 

 conclude that the general character of the zodiacal 

 light is fairly well established. It is almost certainly 

 due to innumerable particles of matter moving round 

 the Sun in elliptic orbits more or less eccentric, their 

 paths lying in or nearly in the plane of the Earth's 

 orbit in a widely extended, but comparatively thin, 

 zone, so that the denser part has the form of 

 a thin, flat sheet, like one of the rings of Saturn, 

 lying partly within and partly without the Earth's 

 orbit. As there is no definite certain limit to the 

 Sun's corona it is possible that the inner part of 

 this sheet is connected with the outer part of the 

 former, and so in a certain sense the zodiacal light 

 might be regarded as an extension of the corona (as the 

 late Sir William Huggins was inclined to think); but 

 this seems an extreme view, for we might similarly 

 regard the planets also as so connected. There 

 are not wanting proofs of the existence of a resisting 

 medium whose influence in former ages upon the 

 planetary orbits is so evident, drawing them inwards 

 and making their paths more nearly circular than 

 would otherwise have been the case ; and though 

 most of the material composing this medium has 

 probably long since fallen upon the Sun and planets, 

 yet there most likely remains enough of it in the vast 

 regions of space separating the larger bodies of our 

 system from one another to become visible to us by 

 reflection of sunlight, and perhaps also by a feeble 

 intrinsic luminosity, like that of the nebulae, as the 

 zodiacal light. 



PHOTOGRAPHIC EFFECT OF CHEMICAL REACTIONS. 



By J. H. VINCENT, M.A., D.Sc, and J. MARLEY, B.Sc, 

 London County Council, Paddington Technical Institute. 



Under the above title, in Mr. Ainsworth Mitchell's 

 Chemical Notes in " Knowledge " for March, 1912, 

 an abstract of a paper by Matuschek and Nenning 

 (Chem. Zeit., 1912, XXXVI, 21) is given and 

 commented on. The results were of such a striking 

 nature and offered so interesting a field for further 

 investigation that we tried many experiments on the 

 same lines. Matuschek and Nenning state that many 

 cases of chemical action are accompanied by the 

 emission of light, which acts on a photographic 

 plate after passing through glass. Our results differ 

 altogether from those obtained by these authors. 

 In a paper on this subject recently published in the 

 Chemical News (March 20th, 1913), we state that 

 " At first some slight photographic effects were noted 

 which could not be traced to known chemical action 

 of the kind studied by Russell, and which is attributed 

 to hydrogen peroxide. These positive results dis- 

 appeared as experience was gained in protecting the 

 photographic plate from the action of extraneous 

 light. As some of the experiments have lasted 

 several weeks, the precautions against the accidental 

 entry of light to the plate cannot be too elaborate. 



In all cases any vapours, and so on, arising from the 

 substances engaging in the chemical action must 

 also be prevented from acting on the plate. Apart 

 from the Russell effect, due to metal screens, and so 

 on, we have been unable to find any evidence of 

 action on the plates. 



The reactions tested were : — 



1. Action of sulphuric acid on zinc. 



2. Action of hydrochloric acid on sodium- 



metasilicate. 



3. Action of nitric acid on lead. 



4. Hardening of plaster of Paris. 



5. Electrolysis of water with platinum 



electrodes. 

 It is difficult to account for the positive effects 

 observed by Matuschek and Nenning. Properly 

 controlled experiments with vessels containing water 

 heated electrically and with paraffin wax heated 

 electrically, have convinced us that the heat produced 

 by chemical action is not competent to account for 

 the apparent positive results. We find then no 

 evidence of any radiation capable of acting on a 

 photographic plate after passing through glass." 



