28 A. Hall on the application of Photography 
rule that, other things being equal, the simpler and more direct 
the method of observing, the better. In order to justify the 
interposition of any new process it must be shown that this 
process gives greater accuracy or greater rapidity of observing 
or both. Thus the chronographic method of observing transits 
is justified on the ground that it gives greater ease and rapidity 
of observing, since the gain in accuracy is scarcely sensible. 
In the case of groups of stars like the Pleiades or Preesepe 
there would be a great advantage in using the photographic 
method provided the plates could be made sufficiently sensitive, 
so that images of stars of the ninth and tenth magnitudes could 
be obtained. Mr. Rutherfurd, who has done so much in as- 
tronomical photography, has made photographs of both the 
groups mentioned, and from his plates Dr. B. A. Gould has 
deduced positions of the stars. Dr. Gould’s memoir on the 
Pleiades was presented to the National Academy five years 
ago, and it is to be regretted that it is not yet published. 
The first application of photography to determine the times — 
of contact in a solar eclipse was made by Mr. Warren De la 
