Secondly, as to the distance of Sirius. Like a few other stars, Sirius lies not quite so far away as to be beyond reach of measurement. No base-line upon earth would cause the slightest seeming change of position in him; but as our earth journeys round the sun, the line from one side of her orbit to the other is found wide enough. A base-line of one hundred and eighty-six millions of miles does cause just a tiny seeming change. It is very little even with Alpha Centauri, and with Sirius it is much less. The “displacement” of Sirius is so slight that to measure his distance with exactness is impossible. Sirius lies more than twice as far away from earth as Alpha Centauri. To reach Sirius, the straight line between earth and sun must be repeated six hundred and twenty-six thousand times. Light, which reaches us from the sun in eight minutes and a half, and from Alpha Centauri in four years and a third, can not reach us from Sirius in less than nine years. Thirdly, as to the size of Sirius. Here, of course, we are in difficulties. Radiantly as Sirius shines on a clear night, and dazzling as he looks through a powerful telescope, he shows no real disk or round surface, but only appears as one point of brilliant light. Some believe him to be much the same size as our sun, while others believe him to be very much larger. But we have no certain ground to rest upon. The only safe method of calculating the probable size--or, rather, weight--of a star is through the discovery of a companion, and a knowledge of its distance from the chief star, and its time of revolution round the chief star. Fourthly, as to the motions of Sirius--not his nightly apparent movement, caused by the earth’s turning on her axis, but his real journey through space. For a long while it was only possible to observe the movements of a star when the star was traveling _sideways_ to us across the sky. A star coming straight towards us, or going straight away from us, would seem to be at rest. Lately, however, by means of that remarkable instrument, the spectroscope, it has been found possible to measure the motions of stars coming towards or going away from us. This is possible as yet only in a few scattered cases, but among those few is the brilliant Sirius. The sideways motion of Sirius had been known before. It now appears that he does not move exactly sideways to us, but is rushing away in a slanting direction at the rate of thirty miles each second, or about one thousand millions of miles a year. How many millions upon millions of miles Sirius must now be farther from us than in the days of the ancients! Yet he shines still, the most brilliant star in the sky. So small a matter are all those millions of miles, compared with the whole of his vast distance from us, that we do not perceive any lessening of light.