604 SCIENTIFIC RECORD FOR 1883 



noinena of fluorescence. And the third is on the maxima and minima 

 of extinction of phosphorescence under the influence of the ultra-red 

 rays. (0. B., January, April, June, 1883, XCVI, 121, 1215, 1853; Ann. 

 Ghim. Phys., V, xxx, 5; Phil. Mag., March, 1883, V, xv, 223; Am. J. 

 ScL, March, 1883, III, xxv, 230.) 



Egoroff has shown that the A and B lines of the solar spectrum are 

 due to the oxygen in the earth's atmosphere. He used a tube 20 meters 

 long, closed by glass plates, filled with dry oxygen under a pressure of 

 15 atmospheres, and observed the calcium light through it. The lines 

 of absorption produced by the oxygen were identical with the A and B 

 of the solar spectrum. (G. B., August, 1883, xcvn, 555; Am. J. Sci., 

 December, 1883, III, xxvi, 477.) 



Langley has published in extenso his valuable memoir on the selective 

 absorption of solar energy, giving the results of his measurements at 

 Allegheny and on Mount Whitney. He has explored the ultra-red 

 region to a wave length of 2.8 microns, the extreme value obtained 

 hitherto being only 1.2. The charts accompanying this memoir are of 

 great interest. (Am, J. iSci., March, 1883, III, xxv, 169 ; Ann. Ghim. 

 Phys., V, xxix, 497 ; J. Phys., II, n, 371.) 



Bayleigh has pointed out the fact that the curve of energy of the dif- 

 fraction spectrum has no special claim to the title of ''normal." A 

 curve plotted with wave-frequencies, or reciprocals of wave-length, as 

 abscissas would have quite as much claim to be considered normal and 

 would give an energy curve more like that obtained with the prismatic 

 spectrum. If the logarithm of the wave-length or the wave-frequency 

 be used as abscissa, a curve will be obtained in which every octave oc- 

 cupies the same space. (Nature, April, 1883, xxvii, 559.) 



4. Interference and Polarization. 



Egoroff, in experimenting with a Chapman grating of 17290 lines to 

 the inch, finds that for every grating and every wave-length there is an 

 angle of incidence such that the reflected diffracted ray coincides with 

 the incident ray. In this case the focus of the grating is infinitely dis- 

 tant. Considering the image of the source of light formed by the re- 

 flecting surface of the grating as the source of light for a transparent 

 grating, it will be seen that the case of the coincidence of the diffracted 

 ray with the incident ray corresponds to the case of minimum devia- 

 tion for this transparent imaginary grating, the angles of incidence and 

 emergence being equal. (J. Soc. Phys. Ghenv. Busse, xrv, 253; J. Phys., 

 December, 1883, II, n, 580.) 



Bowland has published a complete investigation of the theory of the 

 concave grating and has compared the results with those obtained by 

 experiment. He finds that since the radius of curvature of concave 

 gratings is usually great, the distance through which the spectrum re- 

 mains practically normal is also very great. In his instrument this ra- 

 dius is about 21 feet 4 inches, the width of the ruling being about 5.5 





