468 SCIENTIFIC KECORD FOR 1884. 



uess of 2°»™ of a solution of iodine in carbon disulphide containing 

 4 per cent, of iodine, a photogTa.i)h of its spectrum proves tlie non- 

 absorbed light to consist of two bands, one beginning near G and termi- 

 nating in the ultra-violet, the other including the infra-red and extend- 

 ing to a point near D. As the richness of the solution in iodine increases 

 up to 32 iier cent., the former of these bands narrows from both ends, 

 finally becoming a mere strip near /^, while the latter contracts toward 

 the red, the extreme red not being reached by the absorption. This 

 solution, therefore, is very useful in the study of these regions of the 

 spectrum. {Proc. Boy. Soc, xxxiv, 480 ; J. Fhys., March, 1884, II, iii, 

 145.) 



The absorption of the ultra-violet rays by different media has been 

 made the subject of investigation by several physicists. Liveing and 

 Dewar employed as a source of light an induction spark between iron 

 points, a condenser being in circuit, the iron lines furnishing points of 

 reference. The prisms, lenses, and tanks used were of quartz or of 

 rock salt, and the absorbing bodies tried were chlorine, bromine, iodine, 

 sulphurous oxide, hydrogen sulphide, carbon disulphide and tetrachlo- 

 ride, chlorine tetroxide, chrome alum, mica, silver, gold, Iceland sj^ar, 

 &c. The spectra were photographed. (Proc. Boy. Soc, xxxv, 71; J. 

 Phys., May, 1884, II, iii, 218.) 



Soret used a revolving spark-carrier, consisting of two disks, whose 

 axes were at right angles, and whose circumferences carried different 

 metals for producing the spark. The liquid whose absorptive effect 

 was to be studied was contained in a glass vessel closed at bottom 

 by a quartz plate, and the light of the spark, after being rendered par- 

 allel by a quartz lens, passed through this liquid, the thickness of which 

 was varied by the immersion in it of a glass tube having quartz plates 

 at the ends. Beneath this colorimeter was a spectroscope Avith a fluo- 

 rescent eye-piece. After determining the thickness of a liquid required 

 to extinguish any of the metal lines, the author constructed curves 

 having the deviations of these lines as abscissas and the thicknesses of 

 the layers as ordinates, and thus obtained curves for the comparison 

 of the absorption of the substances used. {J. Phys., July, 1884, II, iii, 

 311.) 



Atmospheric absorption has received considerable attention. Lang- 

 ley read a paper before the National Academy, in which he showed that 

 the ordinarily assumed coefficient, about 20 per cent., was too low prob- 

 ably by an amount equal at least to the whole amount in question. 

 The cause of this lies in the assumption by Bouguer's formula, employed 

 by Herschel, Pouillet, and others, that the coefficient of transmission 

 through the atmosphere is a constant. That this is impossible follows 

 jrom the composite character of the radi/ition, as Melloni long ago proved. 

 ]''rora his own reasouiuo-, founded upon the best data he has been able 

 to obtain, the author believes the actual mean absorption of sun and 

 starlight to be not improbably over 40 per cent, at the sea level, {Am, 



