OcrTosBER 18, 1918] 
tion after the war, and the plan of giving 
credit for the intensive war courses toward a 
degree in engineering should be adopted. On 
the other hand, it is reasonably certain that 
the character of the men who complete the new 
engineering courses will be excellent, and the 
colleges should insist upon this high standard 
of scholarship and character after the war.— 
The Electrical World. 
SCIENTIFIC BOOKS 
Annals of the Astronomical Observatory of 
Harvard College. Vol. 79, Part 1. 4°, pp. 
86; Vol. 83, Part 2, 4°, pp. 28; Vol. 91, 4°, 
pp. 290. Edward C. Pickering, Director. 
Cambridge, Mass. 1918. 
The Annals of the Harvard College Ob- 
servatory occupy a unique position in the 
literature of astronomy by reason of their 
great extent and the wide range of subject 
matter included in them. Collectively they 
form an impressive memorial to the indefat- 
igable director who has inspired the produc- 
tion and publication of more than three 
fourths of the four score volumes composing 
the series. In diversity of subject matter, in 
suecessful coordination of effort and in con- 
densed presentation of material the three vol- 
umes briefly cited above are typical of the 
institution from which they come. 
The first of the three, prepared by Leon 
Campbell, contains observations of three hun- 
dred and twenty-three variable stars made 
during the years 1911-16, in continuation of 
a program commenced twenty-two years earl- 
ier. In accordance with the general policy of 
the observatory its purpose is the accumula- 
tion and preservation of reliable data for 
future study of the changes in the amount of 
light received from stars of the class desig- 
nated variables of long period. These changes 
of brillianey are notoriously irregular in char- 
acter and our knowledge of the causes upon 
which they depend is only fragmentary. The 
‘relation between these causes and the data 
furnished by the present volume is committed 
to the future investigator. 
The second volume cited, prepared under 
the direction of Alexander McAdie, lies in the 
very different field of meteorology and con- 
SCIENCE 
397 
tains observations made at Blue Hill Observa- 
tory (Mass.) in the year 1917. Apart from a 
brief preface the work is wholly tabular in 
character and contains both in detail and in 
summarized form the customary meteorolog- 
ical data. 
The last of the volumes named above, pre- 
pared jointly by Annie J. Cannon and Ed- 
ward ©. Pickering is an initial installment of 
the Henry Draper Catalogue of Stellar Spec- 
tra, to be completed in seven more similar 
volumes. For the most part its pages are 
tabular in character and are intended to place 
at the disposal of the theorist, data as ac- 
curate and as extensive as can be derived from 
the great store of Harvard photographs of 
stellar spectra, relative to the spectrum and 
magnitude of a great number of stars, so 
chosen as to be typical of every part of the 
sky. These photographs, taken partly at Har- 
yard and partly in Peru, have been laboriously 
examined and classified by Miss Cannon and 
others and the result of four years of such 
labor is a catalogue showing as its chief data 
the magnitude and the spectral type for more 
than 200,000 stars. The classification is nat- 
urally upon the system originated at Har- 
yard and now in general use, in which for 
the most part, stellar spectra constitute a 
continuous sequence whose chief divisions 
are represented serially by the letters B, A, 
F, G, K, M, with subdivisions of these classes 
upon a decimal system. The physical signifi- 
cance of this series is recognized to be of 
fundamental importance in every inyestiga- 
tion of the larger problems of stellar astron- 
omy. In accordance with its distinctly enun- 
ciated plan that we have noted above, the 
present volume is devoted to the preparation 
of material out of which the implications of 
this series may be worked more perfectly than 
has yet been done. As a contribution to that 
end the introduction to the volume contains 
explicit definition and illustration of each 
spectral class and of many of their subdivi- 
‘ sions, presented in brief but very convenient 
form. 
The three volumes are worthy additions to 
a long line of predecessors whose characteris- 
