“My remarks upon that subject will be very general,” said Mr. Seymour; “I shall explain the principle, without entering into the minutiæ of its applications. The vertical windmill, which is the kind in most common use, consists, as you well know, of an axis, or shaft, placed in the direction of the wind, and usually inclining a little upwards from the horizontal line. At one end of this, four long arms, or yards, are fixed perpendicular to the axis, and across each other at right angles; these afford a surface, on which a cloth can be spread to receive the action of the wind. To conceive why these sails should revolve by the force of the wind, we must have recourse to the theory of compound motion. It is very evident that, if a mill exposed directly to the wind should have its four sails perpendicular to the common axis in which they are fitted, they would receive the wind perpendicularly, an impulse which could only tend to overturn them; there is a necessity, therefore, to have them oblique to the common axis, that they may receive the wind obliquely, when their effort to recede from it causes them to tarn round with the axis; and the four sails being all made oblique in the same direction, thus unite their efforts for the common object.” “You have not yet told us what degree of obliquity the sail ought to make with the wind,” said the vicar. “The same as the kite ought to make, _fifty-four_ degrees and _forty-four_ minutes,” replied Mr. Seymour. “Do you not remember, papa, when we were last in London, you pointed out to us a curious mill on the banks of the river, which went without any sails?” “You allude to the horizontal mill at Battersea.” “I remember it was at Battersea,” observed Louisa; “and I dare say, papa, that you recollect the strange story which the waterman, who rowed us down the river, told Tom and myself. He said ‘that, when the Emperor of Russia was in London, he took a fancy to the neat little church at Battersea, and determined to carry it off to Russia; and that for this purpose he had sent a large packing-case; but, as the inhabitants refused to let the church be carried away, the case remained on the spot where it was deposited.’”