THE PHOTOGRAPH IN ASTRONOMY 
detail from which it could be deduced, 
until photographs of its spectrum made 
at Flagstaff in 1910 and 1911 revealed 
for it a retrograde rotation which it 
accomplishes in a day of about ten and 
three-fourths hours. 
It is from a similar analysis of their 
light that the motions of stars and nebule 
are found. The incandescent condition 
of these bodies makes it possible to 
ascertain the identity of the substances 
of which they consist; and by a com- 
parison of their spectra with that of our 
sun, some knowledge is obtained of their 
state of evolution. Many startling dis- 
coveries result from these investigations, 
especially in case of some of the nebulz 
whose velocities of approach or recession 
are so great as almost to defy belief, 
reaching in several instances, one thou- 
sand kilometers per second. 
213 
In one case at least, that of the nebula 
in Virgo, Dr. V. M. Slipher has detected 
the rotation of this great mass by the 
inclined lines of its spectrum. Another 
interesting and unique spectrographic 
discovery is that the wisplike nebula in 
the Pleiades in all probability shines by 
reflected light received from relatively 
near by stars. This is the only known 
example of a nebula that shines by any 
but its own light. 
Direct photographs of the great Hal- 
ley’s Comet and Comet a 1910 show 
details and the 
their tails which 
stretch from thirty to fifty degrees or 
The cloudlike 
streamers in the tails of these comets 
remarkable structural 
great length of 
more across the sky. 
indicate something of the rapid flow 
away from the head of the mingled 
meteoric and gaseous material, and 
Jupiter, August 11, 1913. 
advisable, since our air is never at its best for long, to make many exposures consecutively, moving the 
plate first laterally and then up and down. 
more one photograph corroborates another 
Photo by C. O. Lampland 
In order to secure the best images of a planet photographically, it is 
We thus get a chance at a good photograph and further- 
