December 29, 1916] 



SCIENCE 



903 



laboratories under varied conditions to 

 reach some conclusions regarding their 

 physical state. The Mount Wilson physical 

 laboratory is doing much valuable work of 

 this kind. 



In the spectra of the solar corona and of 

 nebula? and nebulous stars certain lines 

 are found which do not belong to known 

 elements. This need not indicate any 

 fundamental differences between the life 

 history of such bodies and that of the older 

 stars. Twenty-five years ago Lockyer's 

 views regarding the dissociation of ele- 

 ments in the stars were treated with levity 

 by most physicists and astronomers. To- 

 day such notions are held to be quite ra- 

 tional. The more elementary forms of 

 matter would naturally be of small atomic 

 weight, and hence would diffuse to higher 

 levels than the heavier elements, and might 

 ultimately escape into space. If it were 

 not for the fact that it is held captive in 

 chemical combinations, we should know 

 nothing of hydrogen. Helium first re- 

 vealed itself to us through its solar lines, 

 and would still be otherwise unknown to 

 us were it not for its continuous produc- 

 tion in radioactive processes. The ele- 

 ments giving the spectra of the corona 

 and of the nebula? are presumably of 

 small atomic weight, and are possibly 

 the units out of which more complex 

 known elements are built, in later stages of 

 development; or they may be, conversely, 

 the results of the disintegration of such ele- 

 ments. It is not impossible that in the fu- 

 ture we may detect traces of these elements 

 on the earth or manufacture them by some 

 powerful disintegrative process. Mean- 

 while deductions from known relations be- 

 tween frequencies of the spectral lines, 

 their breadth, and the atomic weight of the 

 elements may give us some clue to their 

 atomic weights. Nicholson has succeeded 

 in constructing hypothetical atoms with 

 given nuclear charges and electron ring 

 systems which give with remarkable accu- 



racy the positions of the lines of the corona 

 and nebula?. Rayleigh showed from kinetic 

 theory and Michelson proved experimen- 

 tally that at low pressures the width of 

 lines may be entirely due to Doppler dis- 

 placements, which vary directly as the 

 square root of the absolute temperature 

 and inversely as the square root of the 

 atomic weight. Buisson and Fabry have 

 verified this law and applied it to the 

 study of nebulae. The width of certain 

 lines, determined from the limit of inter- 

 ference, indicates that the temperature of 

 the Orion nebula is about 15,000 degrees, 

 and that two groups of lines are due to 

 atoms of weights 2.72 and between 1 and 2 

 respectively. This is a remarkable confir- 

 mation of Nicholson's previous conclusion 

 that the emission centers are of atomic 

 weights 2.95 and 1.31. 



During the past ten years the bounda- 

 ries of the known spectrum have been 

 greatly extended in both directions. The 

 difficulties of investigation in the infra- 

 red are very great, but by the methods of 

 reststrahlen and of focal isolation Rubens, 

 working in succession with Nichols, Wood 

 and von Baeyer, has isolated and meas- 

 ured certain regions of great wave-length. 

 The longest wave-length measured is about 

 .3 mm., while the shortest Hertzian waves 

 so far obtained are 2 mm. long. The study 

 of line radiation in this region is even more 

 difficult, but Paschen and his pupil, the 

 American Randall, have succeeded in meas- 

 uring many lines extending to about 90,- 

 000 Angstrom units. 



In the ultra-violet Lyman has extended 

 the region first made known to us by 

 Schumann to a wave-length of about 600 

 Angstrom units. Beyond this point it is 

 difficult to go, on account of absorption, 

 lack of sensitiveness of the photographic 

 plate, and small reflecting power of specu- 

 lum metal. Gratings ruled on silicon and 

 photoelectric detectors may enable us to 

 bridge the gap between these waves and 



