6(5

THE MOON .

they are taken in order from left to right, or from right to left,may serve to indicate the changes of phase during the secondand third quarters of the month respectively.

To those who are familiar with the theory of projections, oreven with the ordinary rules of perspective, the above explanationinvolves no difficulty. To others, we fear, it may be somewhattroublesome to realize that a boundary, which is really circular,may at one time appear to be a straight line, and at othertimes an ellipse of varying degrees of ovalness.

The next point which calls for special attention is, that theMoon always turns nearly the same half of its surface towardsour view; the reason being that it turns once round upon anaxis which is nearly perpendicular to the plane of its orbit,while it travels once round the Earth . We are aware thereare some who still deny this truth, even as there are those stillto be met with whose ideas of parallax encourage them to denythe spherical shape of the Earth . With such we do not wishto argue. But for the sake of others we remark, that to provethe Moon ’s rotation upon its axis, it is sufficient to ask anyone to walk round a circular table, while all the time he keepshis face turned towards its centre. If when he begins to walkround he is looking east, he will be found, when half-wayround, to be looking west, and at two intermediate positionsnorth and south respectively. When half-way round he hasturned his face from east to west, or in other words, he hasturned himself exactly half-way round about a vertical axis;and by the time that he has gone once round the table, he hasalso turned himself through one entire revolution, and haspassed through the four positions, in which his face has re-spectively looked east, north, west, and south; or east, south,west, and north; according to the direction in which he haswalked round the table. In exactly the same way the Moonmust turn once round, or very nearly once round, upon itsown axis, while it goes once round the Earth , in order tokeep very nearly the same face turned towards the Earth ’scentre.

It is simply because this motion round its own axis isuniform, while there is some considerable amount of variation