was not seen. "There was not the slightest room," I wrote in 1872 (and, despite the opinions which have been since expressed by several astronomers, I see no reason for changing my opinion), "for questioning the accuracy of the calculations by which its path had been predicted. Astronomers were certain that, if undestroyed or undissipated, the comet would follow the assigned path—as certain as a station-master would be that a train would enter a station along the line of rails assigned to it, unless some accident or mistake should occur. But comets do not make mistakes, though, as we now see, they are not free from accidents. This comet had already met with an accident, being broken by some mischance into two parts, under the very eyes of astronomers. Possibly in 1859 it met with further misadventures. At any rate, something had happened to the comet since its retreat in 1852. 'It is now,' Sir J. Herschel wrote in February, 1866, 'overdue. Its orbit has been recomputed, and an ephemeris calculated. Astronomers have been eagerly looking out for its reappearance for the last two months, when, according to all former experience, it ought to have been conspicuously visible, but as yet without success—giving rise to the strangest theories. At all events, it seems to have fairly disappeared, and that without any such excuse as in the case of Lexell's, viz., the preponderant attraction of some great planet. Can it have come into contact or exceedingly close approach to some asteroid as yet undiscovered? or, peradventure, plunged into, and got bewildered among, the ring of meteorites, which astronomers more than suspect?'"
But, as I pointed out at the time, there was a convincing objection against the first of these theories in the circumstance that, the two comets into which Biela had separated being more than a million miles apart when they passed out of view in 1852, it was not in the least likely that both would be so far perturbed by asteroidal perturbations as to remain thenceforward undiscoverable. "It would be a singular chance," I said (this was before November 27, 1872, when fresh light, presently to be noted, was thrown on this object), "which should bring one of these objects into collision with a minor planet, or so near as to occasion an important disturbance. But, supposing this to happen, then the fellow comet, not traveling in the wake of the first, but side by side, would certainly have escaped. For it must be remembered that, although 1,250,000 miles is a very small distance indeed by comparison with the dimensions of the solar system, it is an enormous distance compared with the dimensions of the minor planets, some of which have a surface not much greater than that of an English county. The minor planet occasioning the comet's disturbance would presumably be one of the smallest, since it has not yet been detected, and the newly-discovered planets are on the average much smaller than those first detected. Now, the earth herself would have no very marked influence on a comet or meteor passing her at a dis-
