DECEMBER 3, 1897.] 
cess was not available until more than one 
half of the plates had been secured (in 
1881), the serious character of the task of 
merely obtaining the photographs, with all 
the difficulties of the wet process, is suffi- 
ciently apparent. But this labor was small 
relative to that of the subsequent measure- 
ments and computations, which were car- 
ried out rigorously in all respects during 
the past fifteen years. As for the work at 
the micrometer it is stated that two assist- 
ants, alternately measuring and recording, 
could ordinarily measure from thirty to 
thirty-five stars a day. 
Itis, indeed, unfortunate that it was neces- 
sary that so longa time should elapse be- 
fore the publication of the results, for it has 
delayed the recognition of Dr. Gould’s posi- 
tion as the leading pioneer in the applica- 
tion of photography to astronomy of precis- 
ion. It should be recalled that it was 
necessary for him to solve for himself, or 
with the codperation of his friend, Lewis M. 
Rutherfurd, most of the difficulties of ad- 
justment, measurement and computation, 
which have since engaged the attention of 
frequent congresses of the committee of the 
Carte celeste. It was as early as 1866 that 
Dr. Gould presented to the National Acad- 
emy his memoir on the reduction of photo- 
graphie observations, with the determina- 
tion of the position of thirty-nine stars in 
the Pleiades, from measures by Rutherfurd 
on plates he had taken. It is much to be 
regretted that the publication of this memoir 
did not occur until twenty years later. 
On going to Cordoba in 1870 Dr. Gould 
carried with him the photographic object- 
glass which Rutherfurd had so successfully 
used, but to his dismay he found it had 
been broken on the voyage. Thus the work 
was delayed three years, although a hun- 
‘dred plates were obtained with the mended 
objective, then replaced by a new one. Two 
exposures, of about eight minutes, were 
made upon each plate, a slight shift in right 
SCIENCE. 
833 
ascension intervening, so that defects on 
the plates could be distinguished from stars ; 
then a third exposure gave either a trail or 
one point of the trail before the star left the 
photographie field of view, whereby the 
orientation of the plate could be determined. 
Of course, great difficulty was found in se- 
curing accurately circular images, especially 
as the modern plan of a large guiding tele- 
scope was not employed, but ‘plates not 
satisfactory in this respect were summarily 
rejected without hesitation, no record being 
made of them, or numbers assigned.’ 
The measurements were carried out with 
two micrometers constructed by Ruther- 
furd and used by him in his early work. 
The coordinates measured were position- 
angle and distance, referred to some se- 
lected star as center. In some cases, of 
large clusters, several centers were employed, 
but the final positions are in all cases re- 
duced to differences of right ascension and 
declination (4a and 40) from a single central 
star. As each plate contained some stars 
whose position had been determined with a 
meridian circle, the comparison of the cata- 
logue and photographic coordinates fur- 
nished equations of condition from which 
corrections were applied tothe latter. The 
accordance of the separate determinations 
of 4a and 46 on different plates is highly 
satisfactory, and is not exceeded in recent 
measurements of clusters by other astrono- 
mers provided with telescopes and measur- 
ing micrometers of the latest design. Were 
such confirmation longer necessary, the re- 
liability of the photographic method would 
be sufficiently established by the results of 
this volume. 
Dr. Gould expresses the ‘ fear that trust- 
worthy inferences from stellar photographs 
may not be expected in the present condi- 
tion of science and the photographic art,’ 
and hence does not attempt to utilize the 
photographs for photometric purposes, al- 
though approximate magnitudes are as- 
