1.8.C. 38 Procs. of the Asiatic Soc. of Bengal. [N.S., XVIII, 
as that of the alphabet, on account of the readjustment in our 
ideas owing to accumulation of new facts and the revision 
which consequently becomes necessary. 
The Henry Draper Catalogue, now in course of publica- 
tion at Harvard gives in detail the classified spectral type of 
about 222.000 stars in all parts of the sky and forms a mine of 
information on the subject for all investigations. 
. It will be apparent from what has been said how 
enormously the work of our astronomical observatories has 
outgrown, since the introduction of these various methods. 
Many of the problems require years of continual observation 
which is surely beyond the means of a single observatory. 
But, happily, well-planned co-operative methods of attack have 
proved invaluably useful. Itis impossible to over-estimate the 
influence of co-operation in astronomical research by means of 
which results of far-reaching importance are fast accumulating. 
An undertaking of this kind inaugurated in Paris in 1887 had 
for its object the systematic mapping of the positions of a large 
number of faint stars, thus extending the great work of Arge- 
lander and Schonfeld to stars of much fainter magnitudes. 
Eighteen observatories (one of which is the Nizamiah Observa- 
tory at Hyderabad) have joined in the undertaking and are 
producing by photographic methods, catalogues which will 
ultimately give the accurate positions and magnitudes of about 
5 million stars down to the 12th magnitude. The work is now 
fairly advanced and some important information has already 
been obtained. But even more valuable results are expected 
when the survey is completed and the vast amount of material 
Form of the System. 
Considerable information regarding the broad features of 
ee Universe can be gained from a study of the brightness of 
stars, 
