Stars are frequently observed through the head of a comet, which apparently, however, exercises no influence in dimming their lustre. But the stars are commonly seen behind the envelopes or comæ, and very rarely through the nucleus. Nothing is better calculated to exhibit the transparent and tenuous character of comets than observations of this kind, and observers should seek for further opportunities of making them. If the motion of a comet is obviously carrying it in the direction of one of the stars in the field, the observer may determine for himself the approximate time of conjunction by noting the distance between the star and comet and allowing for the motion of the latter. He will then know when to come to his telescope and witness the phenomenon. Should it appear probable that the comet’s nucleus will pass over the star, he should commence his watch some time before it occurs; he may then make comparisons before the star is involved in the outlying nebulosity, and trace the whole event from beginning to end. Any changes in the light or aspect of either star or comet would then be manifested. The comet of 1847 is said to have passed centrally over a 5th mag. star, but the latter was unaffected. Encke’s Comet on one occasion interposed itself directly over one of a pair of 10th mag. stars, but their relatively equal brilliancy suffered no change. Encke’s Comet, however, has no stellar nucleus. The latter feature is so bright and compact as displayed in many other comets, that its transit over a small star must have some effect either in obliterating it altogether, or in detracting from its lustre. Visible evidences of rotation seem to have been suspected in certain comets, but this has never been substantiated on sufficient grounds. The circumstance is one, however, which should be remembered. During a series of observations the observer who notes the details of structure with particular regard to position may discover similar traces, and possibly learn something of the cause. The nucleus of a bright comet should always be examined with a moderately high power, so that any variations or peculiarities of form may be detected.