I do not know, my dear Theophilus, whether you have formed an exact idea of this extent of 38,000,000 leagues, which lie between us and the sun. In general, we can only conceive prodigious distances such as astronomy deals with, by representing them by the interval of time which certain movable bodies known to us would consume in traversing them. Let us then have recourse to comparisons of this kind. A cannon-ball weighing 12 kilogrammes, exploded by 6 kilogrammes of powder, proceeding at a uniform rate of 500 metres a second, would take 10 years to travel from the earth to the sun. Supposing sound to travel at the same rate as on the surface of the air, and at a uniform rate, it would take 15 years to accomplish this journey. If a railway were laid through space between the earth and the sun, a train travelling at express speed, 12½ leagues an hour, would not arrive at its destination until the end of 338 years. This imaginary train, if dispatched from the earth in January, 1872, would arrive at the sun in the year 2210. The light from the sun, which travels 77,000 leagues in a second, takes 7 minutes 13 seconds to reach the earth. _Theophilus._ The distance between the earth and the sun is, then, 38,000,000 miles--that is our unit of measurement for the distances of the stars. Now let us hear about these distances. _The Author._ I will deal first with those stars which are nearest to us. One of these is a star in the constellation of the _Swan_. This star is distant from the earth 551,000 times our unit of measurement, that is to say, that we must multiply 551,000 times the distance of the earth from the sun to represent the distance of the star which we are considering, and yet it is one of the nearest to the earth. If we wish to represent this distance by the time occupied in the transit of light, supposing this light to travel, like that of our sun, 77,000 leagues a second, it would take 9½ years to travel from the star to us. Now, if you wish to know the distance of other stars, and remember that I only speak of the nearest, look at this table, which I found in an astronomical treatise: DISTANCE OF CERTAIN STARS FROM THE EARTH. _Names of the _Distances from _Time of transit Stars._ the Earth._ of light._ α Of the Swan 551,000 times 9 years and a half. α Of the Lyre 1,330,700 21 years. α Of the Great Dog 1,375,000 22 years. α Of the Great Bear 1,550,800 25 years. Polar Star 3,678,000 50 years. Thus, the star α of the Lyre is distant from us more than 1,330,000 times as far as the earth is from the sun, and its light takes 21 years to reach us. If, by any celestial catastrophe, star α of the Lyre were to disappear, to be annihilated, we should still see it for 21 years, as its light takes that time to reach us.