It appeared, from its gradual movement, to lie almost exactly in my course, so that if it were what I suspected, and were not at any great distance from me, I must pass either near or through it, and it would surely explain what had perplexed and baffled me in the case of the former nebula.

At this distance the nature of the cloudlet was imperceptible to the naked eye.

The window telescope was not adjustable to an object which I could not bring conveniently within the field of view of the lenses.

In a few hours the nebula so changed its form and position, that, being immediately over the portion of the roof between the front or bow lens and that in the centre of the roof, its central section was invisible; but the extremities of that part which I had seen in the first instance through the upper plane window of the bow were now clearly visible from the upper windows of either side.

What had at first been a mere greatly elongated oval, with a species of rapidly diminishing tail at each extremity, had now become an arc spanning no inconsiderable part of the space above me, narrowing rapidly as it extended downwards and sternwards.