PHOTOGRAPHIC OBSERVATIONS OF MoREHOUSE’S COMET. 
By W. A. CoGSHALL. 
Comet ¢ 1908 was found on a plate taken at the Yerkes Observatory 
on September ist and has been so situated as to allow observation from 
any point in the northern hemisphere for several hours each night. 
Most of the comets, during the time they are visible to us, are in 
nearly the Same direction from us as the sun, and so are seen only for a 
short time before sunset in the evening, or before sunrise in the early 
morning. 
Comet ¢ had a high northern declination when found, and afterward 
passed within about 16 degrees of the north pole of the sky, so that during 
this time it was visible all night. As a result continuous records were 
secured through several hours, from the time it became dark in Europe 
till daylight in California. 
These records show beyond doubt what has been indicated by several 
other comets—that the tail is composed of matter driven off by the action of 
the sun from the head of the comet, and that the velocity of motion of these 
particles in the tail is such that practically a new tail is formed each day. 
While this comet was not very bright visually, it photographed very 
quickly, exposures of an hour with a short focus lens showing from 6 
degrees to 10 degrees extension of tail, and it also showed unusual and 
sudden changes in the details of its tail. 
The most prominent of these are shown in the accompanying photo- 
graphs. 
The first of these happened on September 30th. The photograph of 
September 29th shows nothing unusual in the appearance of the comet, 
but the next plate whose mid-exposure time was September 30th, 11 hours, 
shows a great change in the size, direction, and general character of 
the tail. This change began during the afternoon of September 30th, and 
by early morning following had produced the appearance shown in the 
plate of September 30th, 14 hours, 45 minutes. 
The great cloud-like mass of tail moved away from the head of the 
comet at a rate of about 20 miles per second, and on the next evening 
