66 W. A. Norton on the Dimensions of Donati’s Comet. 
quently continued on in the tangent to the orbit; it being sup- 
posed that they were subject to no effective action from the sun, 
whether repulsive or attractive. It accordingly appears that not 
far from one-half of the tail, in breadth, on the concave side was 
made up of particles that were not effectively repelled by the sun, but 
separated from the nucleus, after having become disengaged from its 
influence, only because they gravitated toward the sun with less force 
than the nucleus did. It will be seen, in the sequel, that these 
cometary particles, although subject to an effective attractive 
action from the sun, were in all probability expelled from the 
nucleus by a repulsive force, and on leaving its surface had no 
projectile velocity. 
The calculations also show that, except in the immediate vi- 
cinity of the nucleus, the particles on the preceding side of the 
tail left the region of the nucleus several days later than those 
which are at the same distance from the nucleus on the concave 
side. For example, at the distance of about 10,000,000 miles 
we find on the convex side the particle which set out on Sept. 
244-360, and on the concave side the particle which set out on 
Sept. 184-884. 
{t will be observed that the calculations hitherto made, have 
orm, with, as will hereafter be seen, a deficiency of matter 
toward the axis. Regarding it as a hollow conoid its cross 
: id 
represents the cross section at the distance of about 10,000,000 
miles from the nucleus. Its longest diameter is in the plane of 
