PART II.

Distances of the Planets .

We know that the sun’s distance from us is nearly ninety-six millions ofmiles ; but, as we are not accustomed to traverse, or to apply any mode ofmeasurement, to a million of miles, we are not enabled, by our assurance of thefact, or the habitual and fluent repetition of the numbers, to form any distinctnotion of the actual extent spoken of. When we speak of an inch, a foot, ayard, we attach a distinct idea to the expression; we understand the extent, forwe can see it and measure it. If we speak of a mile, of ten miles, a hundredmiles, we also form distinct notions of the distance : in the case of the mile, weare perfectly clear, for we can frequently see it at one glance ; we can, at alltimes, estimate its extent by its number of yards and feet. Of ten, or a hun-dred miles, the mind is tolerably well satisfied ; they are distances we frequentlytravel; extents over which we can, without much effort, apply the precon-ceived scale of a mile, and we are satisfied with the result; we see and feel thatit is an extent over which we can easily pass in the business of life. In thecase of distances of thousands of miles, those alone who have performed longsea voyages make any clear estimate. A person sailing from England to New York forms distinct notions of the distance of one, two, three, or four thou-sand miles, not, as we do in the case of a single mile, by imagining the distanceto be spread before him, but by the distinct impression that he has travelled ata certain known rate during a certain number of days. A traveller of thisclass forms a clear idea even of the circumference of the earth, the distance towhich, as it may be said, his eye is accustomed; he can multiply to the neces-sary extent ; and be satisfied, without painful effort, that he estimates thedistance truly. But the imagination is unequal to any distinct idea of the spaceoccupied by a hundred millions of miles, of the appearance it would exhibit,or how it could be placed within the scope of our faculties of sight and estimate.We will endeavour, in some degree, to familiarize the idea of the extent of thisenormous distance—namely, a hundred millions of miles—by the easiest meanswe possess ; by applying to it our known terms of distance and rate of travel.

If we travel at the rate of ten miles per hour, and continue the progress,without intermission, during each twenty-four hours of the day and night, forthe space of fifteen weeks, we shall have travelled over somewhat more than