mathematical physics? But the reader is to consider, that the ruins made by Lord Rosse, are in _sidereal_ astronomy, which is almost wholly a growth of modern times; and the particular part of it demolished by the new telescope, is almost exclusively the creation of the two Herschels, father and son. Laplace, it is true, adopted their views; and he transferred them to the particular service of our own planetary system. But he gave to them no new sanction, except what arises from showing that they would account for the appearances, as they present themselves to our experience at this day. That was a _negative_ confirmation; by which I mean, that, had their views failed in the hands of Laplace, then they were proved to be false; but, _not_ failing, they were not therefore proved to be true. It was like proving a gun; if the charge is insufficient, or if, in trying the strength of cast iron, timber, ropes, &c., the strain is not up to the rigor of the demand, you go away with perhaps a favorable impression as to the promises of the article; it has stood a moderate trial; it has stood all the trial that offered, which is always something; but you are still obliged to feel that, when the ultimate test is applied, smash may go the whole concern. Lord Rosse applied an ultimate test; and smash went the whole concern. Really I must have laughed, though all the world had been angry, when the shrieks and yells of expiring systems began to reverberate all the way from the belt of Orion; and positively at the very first broadside delivered from this huge four-decker of a telescope. But what was it then that went to wreck? That is a thing more easy to ask than to answer. At least, for my own part, I complain that some vagueness hangs over all the accounts of the nebular hypothesis. However, in this place a brief sketch will suffice.