ball, painted of dark colour, be coated, first with a distempered ochre, and afterwards with a bright yellow: then, with a broad wooden point, let spots of the coloured coatings be taken off, in imitation of the solar spots, then happening to be visible. A ball thus prepared exhibits the actual construction of the atmospheric strata, as indicated by the spots, and will show the three surfacesof the sun’s non-luminous bodyof its reflecting under stratum, and of its resplendent upper stratum.
Now in all this, it is not so much the teaching of astronomy, as the invigoration and replenishment of the prime faculty of the mind, by the aid of astronomical facts, that we intend. An endeavour may be made, with this view, to put the mind into possession of the celestial distances; or at least to impart something better than the vague notion of the heavens as a dome spangled with shining points.
This may be attempted by means of a gradual extension of the sight from nearer to more remote objects, which are at known distances, one from the other, and from the spectator; as thus:The learner is directed, we will say, to look at a farm-house, and a windmill, on the nearer horizon, and three miles apart one from the other. Next, if the locality allows of it, let a three miles be found, marked by two conspicuous objects, and situated on an horizon twenty miles distant; or let the same angular distance be carried from the nearer to the more remote horizon, and the actual interval be ascertained by reference to a county map. If, by these means, a notion has been acquired of the diminution of objects, or intervals, by distance, the question may be putNow, can you imagine, how six hundred miles, measured from the Lizard Point to Pent-land Firth would appear, if you could bring both extremities of the British main at once within view? Hardly. Yet I will show you much more than thisI mean, a full two thousand miles, and rather more, stretched out before
