Chemistry and Physics. 393 



value in 3*125 days. It produces an induced radio-activity, whose 

 rate of decay is such that it falls to a half value in about 35 

 minutes. There are indications of the existence in crude petro- 

 leum of slight traces of a radio-active substance more persistent 

 than the radium emanation. — Phil. 3Iag., October, 1904, pp. 

 498-508. 



13. Absorption of Water Vapor in the Infra-red Solar Spec- 

 trum. — F. E. Fowle, Jr., in No. 1, vol. II, of the Quarterly issue 

 of the Smithsonian Miscellaneous Collection, details the results of 

 a holographic study, made at the Smithsonian Astrophysical 

 Observatory, of the absorption of water vapor in the infra-red 

 region of the solar spectrum. It is shown that "the selective 

 absorption of water vapor, within the range of densities ob- 

 served, seems to depend only on the amount of the absorbent 

 present and is well expressed by Bouguer's formula. In other 

 words, the absorption produced by a given quantity of water in 

 the form of vapor, is the same whether the path is great through 

 a small density or vice versa. Considering successive bands, for 

 example 0*81/*,, par, 3>, \F, O, it may be noted that the selective 

 absorption of water vapor is not greatest like the general absorp- 

 tion at the shorter wave-lengths, but increases as the wave-lengths 

 of the bands increase. It varies from 10 per cent in the more 

 shallow bands near A, at 0'76/x, to nearly 100 per cent in the 

 bottom of O at l*80/x, when only on exceedingly dry days is much 

 indication of energy detected. However, in the separate bands 

 themselves, when the increase in absorption on reaching the bands 

 from the shorter wave lengths side is quite sudden, the absorp- 

 tion then more slowly decreases like the general absorption with 

 increasing wave lengths." 



14. On the Action of Wood on a Photographic Plate in the 

 Dark. — Continuing his work on the action of various sub- 

 stances upon a photographic plate, W. J. Russell shows that 

 this property probably belongs to all wood, some kinds, however, 

 being much more active than others. The sample of wood must 

 remain in contact with, or at a little distance from, the sensitive 

 plate for a time varying from 30 minutes to 18 hours; the tem- 

 perature must not be above 55° C. The wood of conifers is very 

 active and gives definite pictures. A section of a branch of 

 Scotch fir gave an excellent picture showing the rings of both 

 spring and autumn growth ; the former were very active and 

 produced dark rings in the picture, the latter were inactive. If, 

 as has been suggested, hydrogen peroxide, present in the resin, 

 is the cause of the action, it is necessary to assume that the resin 

 in the dark (autumn) rings is under such conditions that it cannot 

 escape. 



Pine wood acted in the same way as the fir ; also the spruces, 

 but with them the action is less definite and sharply marked, and 

 in some cases the dark rings were also active. With larch wood 

 the picture is the reverse of that of the fir, the dark rings being 

 active, the light rings inactive. Of other woods, oak, beech, 



