the potter fashioning an artistic vase from a mass of clay, so do we witness with a higher interest the comet, with all its symmetry and beauty, emerging from a mass of cloud, fashioned by great laws which are only the hands of the Divine Artist, by which it is moulded into the requisite form.
The plate illustrating the structure of the comet's head, is intended to have only a typical significance. In drawing it we have been indebted to the views, by Mr Cooper, of Donati's comet, as seen by him through his great refractor at Markree Observatory. We have combined with these the observations of M. Chacornac, of the Observatory at Paris, in order to illustrate the stratified appearance presented by the successive envelopes.
The particles of which the comet is composed are never motionless; they are in a ceaseless flow, impelled by forces which communicate to them an inconceivable rapidity of motion. The deepest mystery hangs over the nature of these forces, but the phenomena, as witnessed with the aid of the telescope, are easily described. When a comet is first descried in the heavens, it appears as a faint star, with a haze around it. It is often impossible to tell by its mere physical aspect whether it is really a comet. To solve the doubt, the observer must wait a little and see whether it is in motion. This assures him that it is not a mere nebula, and he concludes that it must be a comet. He traces, for a short way, the curve
