224 
The white stars are considered to be in a more 
diffuse state than our Sun, and hence in an 
earlier stage of development. The subdivision 
represented by Bellatrix, which has a char- 
acteristic spectrum of the ‘Orion type,’ is 
placed first in the order of stellar evolution. 
Considerable space is devoted to the question 
of which class of spectrum corresponds to the 
highest temperature of the radiating photo- 
sphere, and numerous lines of evidence are ad- 
duced to support the view that this is found in 
case of the stars with spectra of the solar type. 
The argument based upon the relative exten- 
sion of the continuous spectrum into the ultra- 
violet region, the extension of the solar type 
being regarded by the authors as the greatest, 
is-not wholly convincing, as the difficulty of 
securing identical conditions of exposure, at- 
mospheric absorption, etc., in the case of dif- 
ferent stars of different types, is very great. 
But emphasis is well placed upon the im- 
portance of taking into account more fully 
than has hitherto been done the large diminu- 
tion in the star’s effective radiation from the 
integrated effect of the selective absorption of 
its atmosphere; that is, from the absorption 
represented by the very numerous dark lines 
in spectra of the solar type. 
Attention is drawn to the important effect 
of the convection currents in stellar atmos- 
pheres, and their increasing activity in the 
region where the dark lines originate, as the 
stars advance in age. This increase is assigned 
as a possible cause of the diminished promi- 
nence of the hydrogen lines in the spectra of 
the second and later types. 
The reasons for the presence of certain par- 
ticular lines of certain particular elements in 
the spectra of stars at different stages are con- 
sidered by the authors to lie in the conditions 
of the absorbing region, as to density and com- 
position, particularly the mixing of various 
vapors. The absence of the metallic lines from 
the spectra of the first type is attributed in 
part to the slight convectional effects in the 
very diffuse atmospheres of these stars, so that 
as a result of diffusion hydrogen and the lighter 
elements preponderate in the region where 
absorption occurs; and in part to a slow tem- 
perature gradient, so that the vapors just above 
SCIENCE. 
[N. 8S. Von. XIII. No. 319. 
the photosphere might differ in temperature too 
little from the photosphere for their lines to be 
seen as dark on the continuous spectrum. 
The effect of density of the vapor is quite 
fully considered, particularly in connection with 
the laboratory experiments of the authors on the 
behavior of the calcium lines. 
The twelve half-tone plates which illustrate 
the volume are admirably done, and represent 
extended and skilful work by the authors in 
their arrangement. Plate II. contains repro- 
ductions of numerous ‘historical spectra,’ as 
they are well named, obtained by the authors 
between 1876 and 1895. ‘These are fully de- 
scribed in Chapter VII. The remaining plates 
receive a ‘preliminary discussion’ in Chapter 
VIII. 
The treatment of the subject as a whole is 
qualitative rather than quantitative, and is not 
mathematical, so that the general reader can 
follow the clear and philosophical reasoning of 
the authors without the necessity of a previous 
familiarity with technical symbols. 
Artistic head pieces and initials appropriate 
to the subject, the hand work of Lady Huggins, 
complete the adornment of the volume. The 
work has received the Actonian prize of the 
Royal Society, and the election of Sir William 
Huggins to the presidency of the Royal Society 
at this time will be recognized as highly appro- 
priate. 
Epwin B. FRost. 
Annual Report of the Chief of the Bureau of Steam 
Engineering of the U. S. Navy Department, 
1900. Washington, Government Printing Of- 
fice. 1900. 8vo. Pp. 128, pl. 17, folded. 
This report, apart from its importance as 
detailing the work in applied science of one of 
the most important bureaus of the U. 8. Gov- 
ernment, has a peculiar interest at the moment 
to all who have become aware of the tendency ~ 
illustrated, for example, in the operation of the 
National Observatory and of the Coast Survey, 
toward amateurism in all branches of the Gov- 
ernment service. The Engineer-in-Chief of the 
Navy, Admiral Melville, is one of the most 
competent expert professionals in the Navy, or 
outside it, in his department, and his report, 
while giving an admirably condensed account 
