PROGRESS IN ASTRONOMICAL PHOTOMETRY. 
155 
of the revolving bodies. It seems to be too soon, however, 
to say anything definite on these causes. 
4. Charts for variable stars have been recognized as a 
necessity ever since the appeal of Argelander to amateur 
astronomers to cooperate in this new field. The Bonn 
Durchmusterung is not in everybody’s hand. Therefore 
the societies which have been formed in England and in 
Germany for amateurs have tried to circulate cheap repro¬ 
ductions of certain parts of these charts which contain vari¬ 
able stars. In England Colonel Mark wick is in charge of 
this branch, and Plassmann in Germany. From the latter 
we have here a copy of the circulated charts (slide). 
In America Professor Pickering has long ago distributed 
a sheet, with 16 small charts, for circumpolar variables in 
the natural size from the BD. Recently he offered single 
sheets, with one variable each, 3° square, and enlarged three 
times, of which the following is a copy (slide). 
The most interesting point I have to mention is a dis¬ 
covery of some engraved charts made by Pogson. Two 
years ago I was able to publish in the Monthly Notices (vol. 
59, 1898) a “ Note on Pogson’s manuscripts relating to his 
proposed atlas of variable stars.” These MSS. are preserved 
at the Harvard College observatory, and contain 134 cata¬ 
logues and 18 charts, for as many variables. Pogson had 
worked over thirty years at this atlas in England and in 
Madras, but nothing was ever heard of printed charts, until 
quite recently six engravings of these charts were sent to 
me. Four of these charts belong to variables which are 
comprised in the atlas lately issued from the Georgetown 
College observator}L It will be seen that Pogson’s area for 
inserting the faintest stars, which he calls of the twelfth or 
thirteenth magnitude, is seven times as great as that on our 
own charts. These four charts and the corresponding four 
of the Georgetown atlas were shown on the screen. 
22—Bull. Phil. Soc., Wash., Vol. 14. 
