On the 17th of March a silvery ray, some 40° long and slightly curved at its extremity, shone out above the sunset clouds in this country. No previous intimation had been received of the possibility of such an apparition, and even astronomers--no lightning messages across the seas being as yet possible--were perplexed. The nature of the phenomenon, indeed, soon became evident, but the wonder of it did not diminish with the study of its attendant circumstances. Never before, within astronomical memory, had our system been traversed by a body pursuing such an adventurous career. The closest analogy was offered by the great comet of 1680 (Newton's), which rushed past the sun at a distance of only 144,000 miles; but even this--on the cosmical scale--scarcely perceptible interval was reduced nearly one-half in the case we are now concerned with. The centre of the comet of 1843 approached the formidable luminary within 78,000 miles, leaving, it is estimated, a clear space of not more than 32,000 between the surfaces of the bodies brought into such perilous proximity. The escape of the wanderer was, however, secured by the extraordinary rapidity of its flight. It swept past perihelion at a rate--366 miles a second--which, if continued, would have carried it right round the sun in _two hours_; and in only eleven minutes more than that short period it actually described half the _curvature_ of its orbit--an arc of 180°--although in travelling over the remaining half many hundreds of sluggish years will doubtless be consumed. The behaviour of this comet may be regarded as an _experimentum crucis_ as to the nature of tails. For clearly no fixed appendage many millions of miles in length could be whirled like a brandished sabre from one side of the sun to the other in 131 minutes. Cometary trains are then, as Olbers rightly conceived them to be, emanations, not appendages--inconceivably rapid outflows of highly rarefied matter, the greater part, if not all, of which becomes permanently detached from the nucleus.