224 
POPULAR SCIENCE REVIEW. 
very beautifully executed chromo-lithographs, is, as regards its contents, 
entirely of an algebraical character. The author deduces, however, from his 
investigations the following condensed results : (1) The absence of the lines 
of some element in the spectrum of a self-luminous body (star) does not 
prove the absence of this substance. (2) The layer in which the inversion 
of the spectrum takes place differs for every body, and that layer is placed 
the nearer to the centre of the star according to the greater vapour density 
and emissive power of the substance which yields the spectrum. (3) This 
layer is, cceteris paribus, nearer to the centre of different stars according as 
the intensity of the gravitation thereof is greater. (4) The distances of the 
layers of conversion of the simple bodies (emitting spectra) from each other, 
as well as from the centre of the stars, increase with an increase of tempera- 
ture. (5) The spectra of different stars are, ccpteris paribus, the richer in 
spectrum lines according to the lower temperature and the greater mass of 
the stars. (6) The great difference observed in the intensity of the dark 
lines of the solar spectrum and that of other fixed stars does not simply 
depend upon the difference of the power of absorption, but also upon the 
difference of depth wherein the inversion of the respective spectra takes place. 
A Topographical Survey of the Hawaian Islands has been ordered by the 
Legislature of the Islands, says Silliman’s “American Journal” (January), 
and an appropriation of $5,000 made for procuring instruments and meeting 
the expenses of the first year. Professor W. D. Alexander of Oahu has been 
appointed Surveyor-General, and is making arrangements for commencing 
the work. He proposes to measure a base line on the sandy isthmus 
between East and West Maui, which is six or seven miles wide, and to cany 
forward the survey as nearly as possible after the methods of the U.S. Coast 
Survey. Geological and botanical collections and observations will be made 
in connection with the survey. 
The Spectrum of the Aurora Borealis. — This has been well investigated by 
Mr. John Browning, who gives his results in the “Monthly Notices of 
the Royal Astronomical Society ” (November 11). During the display of 
the Aurora Borealis which occurred on the evenings of October 24 and 25, 
he confined his attention to observing the spectra of the light, taking it in 
different parts of the sky. When the spectroscope was directed to the more 
luminous portions, which were generally of a silvery white, the spectrum 
appeared to consist of only one line. He could not succeed in verifying the 
position of this line ; but it appeared to be situated between D and E in the 
spectrum. When observing the light of the red portions of the sky, a faint 
r$d line became visible. He had no means of verifying the position of these 
lines with any degree of exactitude ; but he was able to throw into the field 
of view a faint continuous spectrum from a distant light, and also the bright 
yellow sodium-line produced by a spirit-lamp. The colour of the green line 
was very peculiar ; had he not been able to observe it by comparison, he 
could not have formed any idea of its position. It was an exceedingly light 
silvery green, or greenish-grey, and often seemed to dicker. Besides the two 
lines particularly described, he occasionally suspected others, one in the red 
and one in the blue ; but he could not be at all sure of this. The colour 
of the light of the aurora seen over the greater portion of the heavens 
resembled exactly that of the discharge of electricity from an induction-coil 
through a vacuum formed from atmospheric air. 
