reached even yet. Plates could easily be handled if the sensitiveness
were increased tenfold. A vast increase in the results may be
anticipated with each improvement of the plates in this respect.
Apparatus for testing plates, which is believed to be much more accurate
than that ordinarily employed, is in course of preparation. It is
expected that a very precise determination will be made of the rapidity
of the plates employed. Makers of very rapid plates are invited to send
specimens for trial.

The photographic work has been done by Mr. W.P. Gerrish, who has also
rendered important assistance in other parts of the investigation. He
has shown great skill in various experiments which have been tried, and
in the use of various novel and delicate instruments. Many of the
experimental difficulties could not have been overcome but for the
untiring skill and perseverance of Mr. George B. Clark, of the firm of
Alvan Clark & Sons, by whom all the large instruments have been
constructed.

The progress of the various investigations which are to form a part of
this work is given below:

1. _Catalogue of Spectra of Bright Stars_.--This is a continuation of
the work undertaken with the aid of an appropriation from the Bache
fund, and described in the Memoirs of the American Academy, vol. xi., p.
210. The 8 inch telescope is used, each photograph covering a region of
10° square. The exposures for equatorial stars last for five minutes,
and the rate of the clock is such that the spectra have a width of about
0.1 cm. The length of the spectra is about 1.2 cm. for the brighter, and
0.6 cm. for the fainter stars. The dispersion of the scale proposed
above is 0.1.