[ 696 J 
LXV. 
THE APPARENT COMETARY NATURE OF THE SPIRAL 
NEBULA IN CANES VENATICI. By W. EH. WILSON, 
F.R.S. (Puate XXI.) 
[Read Novemser, 17; Received for Publication Novemper 19 ; 
Published Frpruary 10, 1898. | 
Tus extraordinary Nebula was discovered by Messier in 1772. 
He described it as a faint double Nebula whose centres are 4’ 35” 
apart, but with its borders in contact. Sir John Herschel observed 
it; but the late Earl of Rosse, using his 6-feet reflector, was the 
first to draw its wonderful spirals. The photograph, which is here 
reproduced, was taken taken in February, 1897, with my reflector 
of 2 feet aperture and 10 feet 6 inches focus. The plate used was 
Cadett’s “ Lightning” brand, and the exposure was carried on for 
90 minutes. If the photograph is carefully examined, it will be 
seen that, in many places, the nebulous matter is condensing into 
knots on the great spirals; and what is most remarkable is that 
these knots are nearly all provided with cometary tails. La Place, 
in his famous Nebular Hypothesis, assumes that the stars have been 
formed from masses of nebulous matter which gradually condenses 
by the action of gravity, and in the lapse of ages forms a central sun. 
From the curves of these spiral nebule, is it not more probable 
that we here have repulsive forces at work, and not a streaming in 
of matter under the action of gravity ? 
These spiral nebule seem to be a distinct class in themselves. 
In all the other types of nebule, such as the “ Dumbbell,” the 
“Crab,” the “ Ring” nebulae in Lyra, and many others, we can 
see no evidence of the forces which are at work in the spirals. 
I think the fact that we see these supposed tails where the 
nebulous matter is condensing into knots on the spirals, is a strong 
point in favour of repulsive action. It isdifficult to see how, even 
supposing the main spirals to be due to a vortex motion, these 
secondary tails could be due to anything but a repulsive force. 
