loyed. 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 deg. 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.

The spectra of all stars of the sixth magnitude and brighter will
generally be found upon these plates, except in the case of red stars.
Many fainter blue stars also appear. Three or four exposures are made
upon a single plate. The entire sky north of -24 deg. would be covered
twice, according to this plan, with 180 plates and 690 exposures. It is
found preferable in some cases to make only two exposures; and when the
plate appears to be a poor one, the work is repeated. The number of
plates is therefore increased. Last summer the plates appeared to be
giving poor results. Dust on the prisms seemed to be the explanation of
this difficulty. Many regions were reobserved on this account. The first
cycle, covering the entire sky from zero to twenty-four hours of right
ascension, has been completed.

The work will be finished during the coming year by a second cycle of
observations, which has already been begun. The first cycle contains 257
plates, all of which have been measured, and a large part of the
reduction completed. 8,313 spectra have been measured on them, nearly
all of which have been identified, and the places of a greater portion
of the stars brought forward to the year 1900,