FEBRUARY 8, 1901. | 
should be as infrequent and as brief as 
possible. 
A Cramer ‘crown’ plate placed in a 
printing frame under a thin or fast print- 
ing positive, will yield a negative picture 
when held for one second at a distance of 
three meters froma 16-candle incandescent 
lamp. The exposure may be gradually in- 
creased to au exposure of an hour at a dis- 
tance of one meter from a 300-candle Pack- 
ard incandescent lamp. How much longer 
the exposure may be is not yet known. All 
exposures up to three and a half minutes at 
a distance of one meter from the 300-candle 
lamp can be developed as fine negatives in 
‘the dark room. This last exposure may 
also be developed as a positive in light 
somewhat feebler than direct midwinter 
sunlight in St. Louis. With greater expo- 
sures, the illumination of the light room 
must be decreased, in order to obtain the 
best results. With the highest exposures 
producing developable results, the plate 
must be developed in the dark room. 
The actinic values-over this vast range 
are now being measured. The plates as de- 
veloped are laid in proper position upon a 
series of large tables, about 40 feet in 
length. The coordinate values determining 
the position of the plate upon the tables 
are, exposure and illumination of the de- 
veloping room. 
The point which itis desired to urge in 
this communication is, that in the coming 
eclipses of this year and next, there is no 
need of losing any plates from over-expo- 
sure, even if they are exposed during the 
entire time of totality. It is hoped that 
this communication will cause those who 
are to take part in that work to lose no 
time in becoming familiar with the possi- 
bilities of development in a bath such as 
has been here described. 
This communication has been prema- 
turely published in order to direct the at- 
tention of those who are to take part in the 
SCIENCE. 
209 
observations of the next eclipse toa matter 
which may have great importance. It 
may be that some of the statements may 
require modification. For example, it is 
perhaps questionable whether exposure in 2 
printing frame at a distance of a meter froin 
a 300-candle lamp for three and a half min- 
utes is an over-exposure of 2,000 times.* It 
is certainly a very great over-exposure. 
Francis EK. NipHir. 
WASHINGTON UNIVERSITY. 
THE PROBABLE SUCCESSORS OF CERTAIN 
NORTH AMERICAN PRIMATES. 
Tue credit for the discovery of the affin- 
ities of the fossil Primates of the Hocene 
deposits of this country have been variously 
claimed by both Marsh and Cope. Leidy, 
however, appears to have clearly preceded 
both these investigators in this respect in 
his ‘ Vertebrate Fauna of the Territories,’ 
published in 1873. In this work, in de- 
scribing the lower jaw of Northarctus tene- 
brosus, a fossil monkey from the Bridger 
Eocene, he makes the following significant 
remarks: ‘‘In many respects the lower 
jaw of Northarctus resembles that of some of 
the existing American monkeys quite as 
mueh as it does that of any of the living 
pachyderms. Northarctus agrees with most 
*Since writing the above it has been found that 
potassium bromide will do all that has been done 
with hypo as above described. The earlier failures 
in the use of bromide were due to insufficient quan- 
tity. In developing some good pictures near the 
zero condition a ten-per-cent. solution of bromide 
has formed a sixth of the bath. The bromide pic- 
tures are somewhat more brilliant, but do not seem 
so sharp and hard as some obtained by hypo. It may 
safely be stated that any camera exposure, from the 
shortest possible, to those lasting for hours, may be 
developed into a good picture. When the exposure 
is too great for development in the dark room as neg- 
atives, the plate may be as successfully treated in the 
light room and developed as a positive. A plate 
which will develop as a beautiful positive in the 
light of a 16-candle lamp, will develop a foggy 
mongrel picture, partly positive and partly negative 
in a perfectly dark room. 
