used formerly to be the case.  Of course this may be explained by the fact that the moon is now moving more swiftly than of yore, but it is obvious that an explanation of quite a different kind might be conceivable.  The moon may be moving just at the same pace as ever, but the length of the day may be increasing.  If the length of the day is increasing, then, of course, a smaller number of days will be required for the moon to perform each revolution even though the moon’s period was itself really unchanged.  It would, therefore, seem as if the phenomenon known as the lunar acceleration is the result of the two causes.  The first of these is that discovered by Laplace, though its value was overestimated by him, in which the perturbations of the earth by the planets indirectly affect the motion of the moon.  The remaining part of the acceleration of our satellite is apparent rather than real, it is not that the moon is moving more quickly, but that our time-piece, the earth, is revolving more slowly, and is thus actually losing time.  It is interesting to note that we can detect a physical explanation for the apparent checking of the earth’s motion which is thus manifested.  The tides which ebb and flow on the earth exert a brake-like action on the revolving globe, and there can be no doubt that they are gradually reducing its speed, and thus lengthening the day.  It has accordingly been suggested that it is this action of the tides which produces the supplementary effect necessary to complete the physical explanation of the lunar acceleration, though it would perhaps be a little premature to assert that this has been fully demonstrated.

The third of Professor Adams’ most notable achievements was connected with the great shower of November meteors which astonished the world in 1866.  This splendid display concentrated the attention of astronomers on the theory of the movements of the little objects by which the display was produced.  For the definite discovery of the track in which these bodies revolve, we are indebted to the labours of Professor Adams, who, by a brilliant piece of mathematical work, completed the edifice whose foundations had been laid by Professor Newton, of Yale, and other astronomers.

Meteors revolve around the sun in a vast swarm, every individual member of which pursues an orbit in accordance with the well-known laws of Kepler.  In order to understand the movements of these objects, to account satisfactorily for their periodic recurrence, and to predict the times of their appearance, it became necessary to learn the size and the shape of the track which the swarm followed, as well as the position which it occupied.  Certain features of the track could no doubt be readily assigned.  The fact that the shower recurs on one particular day of the year, viz., November 13th, defines one point through which the orbit must pass.  The position on the heavens of the radiant point from which the