I20 



KNOWLEDGE & SCIENTIFIC NEWS. 



[June, 1905. 



property. The reduction of the silver was also found 

 to be effected by vegetable substances with a strong 

 odour, such as coffee, brandy, and linseed oil, which 

 contain compounds, terpenes, allied to turpentine. 



Dr. Russell attributed the phenomenon to the action 

 of hydrogen peroxide formed by the oxidation of these 

 terpenes in the presence of water (see " K.nowledge 

 .■\.\D Scientific News," this vol., p. 100). 



Dr. Sperber, however, held a different theory and 

 concluded from the results of a simple experiment that 

 the action of the turpentine was due to photo-chcniically 

 active radiations. He found that when three plates 

 were placed horizontally on a skeleton stand under a 

 bell-jar with the bottom and middle plate film upper- 

 most and the top plate film downwards, while a dish of 

 turpentine was placed on the middle plate, all the films 

 were completely blackened after four days. The ex- 

 periment was now repeated with the position of the 

 films reversed, so that the top plate was film upwards 

 and the other two film downwards. In this case only 

 the edges of the films were darkened, although the jar 

 was equally full of turpentine vapour, and there would 

 thus be the same possibility of chemical reduction. iXc- 

 cording to the radiation theory, only the edges of the 

 plates in the second experiment would receive reflected 

 rays from the wall of the bell-jar, whereas in the first 

 experiment the rays would strike directly on the upper 

 film and be reflected directly on to the lower films. 



Last year Dr. von .'\ubel showed that various resin- 

 ous substances could affect a photographic plate 

 through black paper, but that the property was lost on 

 heating the substance above its melting point. 



Prior to this, experiments had been made by Mr. 

 Hepworth and the writer to determine whether the 

 " fogging " phenomenon mentioned above might not 

 be due to the presence of resinous constituents of the 

 wood, and it was found that many different kinds of 

 wood possessed the property of so affecting a photo- 

 graphic plate in the dark that when developed in the 

 usual manner a good impression of the section of wood 

 was obtained. 



Later in the year Dr. Russell communicated to the 

 Royal .Society the results of his very complete experi- 

 ments on the same lines. He found that the impression 

 was formed in 30 minutes to 18 hours, and that differ- 

 ent kinds of wood showed great differences in their 

 behaviour. Thus conifer woods were particularlv 

 active, as was also the case with oak, beech, .Spanish 

 chestnut, sycamore, and rosewood, while elm, ash, 

 hor.se chestnut, and plane had but little action on Ihu 

 plate. liut these relatively inactive woods could be 

 rendered active by exposing them beforehand to sun- 

 light or to blue rays, and this treatment also rendered 

 the active woods still more active. Larch gave inter- 

 esting pictures, the dark rings of the wood being 

 active and the light rings inactive, while the reverse 

 was the case with .Scotch fir. The true bark of a tree 

 and al.so the pith were found to be entirely inactive, but 

 very old wood and bog wood had retained their activity. 



In the present writer's experience very dry wood is 

 less active than that which has been in :i moist atmo- 

 sphere. The effect produced by a piece of old very 

 dry oak is shown in the accompanying figure. The 

 piece of wood was left for several days on a Barnet 

 medium plate enclosed in a well-fitting cardboard box 

 in the dark room. As it had app;ircntlv had no effect, 

 the experiment was repeated, and the plate developed 

 after a year. 



The print is interesting as showing certain features 



not seen in the beautiful pictures obtained by Dr. 

 Russell. There is a curious halation round the edges 

 of the wood which seems to indicate that the cross 

 section of the grain is more active than the longitudinal 

 section. It also shows that wood that is apparently 

 inactive may give an impression if left for a very long 

 period. 



Oak left in contact with Photographic Plate- in the darlv for a year. 



Herr G. Lunn has recently shown that a straw- 

 board box is radio-active, the rays apparently proceed- 

 ing from a number of points over the surface so that 

 they form an irregular outline of an object placed upon 

 a photographic plate in the box. The board becomes 

 spent after an experiment, but recovers spontaneously 

 if left to itself. 



Here, again, it is probable that resinous substances 

 are the active bodies, but further experiments are re- 

 t|uired to determine whether hydrogen peroxide is 

 formed and plays the part of an intermediate agent in 

 any of these phenomena. 



A Bird-like Flying 

 MoLchine. 



By F. W. 11. Ill TciiiNso.v, .M..\., H.Cii. (C.wtah.). 



' A Paper read before the Cambridge University Engineering 

 Society. ) 



To those who have not given .'ittention to the structure 

 of a bird's wing, the following rough description may 

 be of interest. The wing of a bird may be regarded 

 as having two portions, (i) That part to the outer 

 side of the wrist joint. The main feathers of this por- 

 tion arc usually about 10 in number and are known as 

 the primary feathers. (2) That part to the inner side 

 of the wrist joint which may be called the body of the 

 wing. The main feathers of this portion vary accord- 

 ing to the length of wing. 



(a.) A salient characteristic of a bird's wing as a 

 whole is the comparatively rigid and heavy anterior 

 edge, and the light, yielding, elastic posterior margin. 



