The interest aroused by these irregular and chaotic nebulous forms is still further increased by the phenomena of the spiral or convoluted nebulæ with which the giant telescopes of Lord Kosse and Mr. Bond have made us further acquainted. As a rule, there stream out
Fig. 5.
Spiral Nebula in Canes Venatici.
from one or more centres of luminous matter innumerable curved nebulous streaks, which recede from the centre in a spiral form, and finally lose themselves in space. Fig. 4 represents a nebula in the form of a sickle or comet-tail, and Fig. 5 shows the most remarkable of all the spiral nebulæ, situated in the constellation Canes Venatici.
Fig. 6.
Transition from the Spiral to the Annular Form.
It is hardly conceivable that a system of such a nebulous form could exist without internal motion. The bright nucleus, as well as the streaks curving round it in the same direction, seems to indicate
