12 



KNOWLEDGE & SCIENTIFIC NEWS. 



[January, 1907. 



After a larg-c luiiiibcr of experiments, the Powell 

 Wood Process Syndicate, Ltd., of 28, Fleet Street, 

 London, K.C, claim to have at last solved the problem. 

 By the Powell process the wood is boiled in a 

 saccharine solution to which is added certain substances 

 obnoxious to terniiles, though the_v are otherwise per- 

 fectly inodorous and innocuous. ' In the subsequent 

 coolintj the solution is absorbed by the tissues of the 

 wood, with the result th;it the "wood is not only 

 strengtht-nod .ind iinpnned in c|u:ility, owing to the [jre- 



sence of saccharine matter, but is also proof against 

 both insects and fungoid growth. Wood thus treated 

 has been buried in ants' nests and placed in various 

 positions open to attack, but in every case it has en- 

 joyed complete immunity, while untreated pieces of the 

 same wood, either attached to the processed specimens 

 or placed around it, have been consumed. 



The news of this discovery will be received with 

 acclamation in many parts of the world, as it will enable 

 local timbers to be employed for constructional and 

 other work, especially as the process will effectually 

 season the wood within a few days of its being cut 

 down. 



The Pleiades. 



This photograph, taken by Prof. Max Wolf in 1902, 

 show s the arrangement of stars in the Pleiades with the 

 curious light inner nebula?. The discovery of the 

 nebulous formation, which seems to extend to the whole 

 group, 'ranks" (according to Miss Gierke) "among 

 the most imjiortant achievements of celestial photo- 

 graphy." 



Tlie photograph was taken with the 16-inch Bruce 

 telescope at Heidelberg, with an exposure of five hours. 

 It has been enlarged from the original negative 3j 

 times, and has not been re-touched. 



Next month will be commenced a series of articles on 

 " Aerodynamics and the Theory of the Aeroplane," by 

 Major Baden-Powell, which should prove of interest at 

 the present time. 



SCIENCE YEAR BOOK. 



0.\E of the star maps in the first issue of the Science 

 Year Book was wrongly printed, the blue portion not 

 corresponding with the black. In the later edition this 

 has been rectified, but any purchaser having a copy 

 with the inaccurate chart, and who will apply to the 

 office, will be supplied with a fresh page to replace it. 



Photography. 



Pure and Applied. 



By Chapman Joni;s, I'.LC, F.C.S., &c. 



Ti... i»j *i ^''" 'I'l'' ^^i'cn known for about a hundred 

 I he Induction , , -r r , , ■ 



Period years that il ;i moist nuxture of chlorme 



and hydrogen is exposed to light the 

 two gases combine to form hydrochloric acid, ex- 

 plosnely If ilu' liylH is very bright, such as sunshine, 

 or quiolly .-ind gradually if the light is more subdued. 

 It is just about fifty years ago that Bun.sen 

 and Roscoc used such a mixture of gases to discoxcr 

 1h)w the amount of chemical change produced in it 

 was affected by variations in the acting light. i?ut 

 when light falls upon such a mixture, the change docs 

 not start at once, and it may be a few seconds up to 

 even a few hours Ijefore the maximum rate of change 

 that a given light can produce is attained. Or, in other 

 words, the mixture of gases appears at first to be 

 quite insensitive, and when the action begins, it grad- 

 ually increases its sensitiveness. This " induction 

 period " has been ascribed to a resistance to combina- 

 tion inherent in one or both of the gases, or in some 

 other way to a change that must precede combination 

 to make it possible. It has been suggested that this 

 change might be either of a chemical or of a merely 

 physical character. 



Recent investigation by Messrs. C. H. Burgess and 

 D. L. Chapman shows that this "induction period" 

 is sometimes, and probably always, due to some im- 

 purity that the chlorine acts upon more readily than 

 upon the hydrogen, or that in some other way prevents 

 the combination of the chlorine and hydrogen. These 

 investigators state that " no evidence can be obtained 

 of a period of photo-chemical induction with a moist 

 mixture of chlorine and hydrogen in the absence of 

 impurities. . . ." Therefore it appears that all 

 arguments founded on the supposed existence of this 

 "induction period," and the analogies that have been 

 drawn from it, fall to the ground. It would be possible 

 to found certain arguments on its non-existence as to 

 the nature of the developable image, but I do not think 

 that they would have any value, as there is no proof 

 that the two cases are analogous. 



The Mechanical 



Action of 



Light. 



The British Journal of Flwtograpliy 

 (p. 970) gives an account of a paper by 

 F. -Alefeld, in the Clieinikcr Zcituitg, in 

 which he describes how he has obtained 

 results that appear tO' indicate that when solutions of 

 certain substances are evaporated so as to form a film, 

 dried at 100° C. for 15 to 30 minutes, and then exposed 

 under a negative for about half an hour to bright sun- 

 shine, the substance so moves about that it accumulates 

 where subjected to light at the expense of those parts 

 that are shielded from the light. The thio-resinates are 

 generally used in an appropriate solvent (water solu- 

 tions will not work soi well), choosing one that leaves 

 on ignition an oxide that will colour glass. The ex- 

 posed film is then heated sufficiently to cause the oxide 

 to combine with the glass. Sharp pictures are so pro- 

 duced, but the whites are never pure, i.e., the substance 

 never completely leaves the parts shielded from light. 

 A second exposure under another negative does not 

 obliterate the effect of the first exposure, perhaps 



