[ [22] The author here means to compare the different quickness of the motion of the head and the heel, when employed in the same action of jumping; and he states the proportion of the former to be three times that of the latter. The reason he gives for this is in substance, that as the head has but one motion to make, while in fact the lower part of the figure has three successive operations to perform at the places he mentions, three times the velocity, or, in other words, three times the degree of effort, is necessary in the head, the prime mover, to give the power of influencing the other parts; and the rule deducible from this axiom is, that where two different parts of the body concur in the same action, and one of them has to perform one motion only, while the other is to have several, the proportion of velocity or effort in the former must be regulated by the number of operations necessary in the latter.
[ [23] It is explained in this work, or at least there is something respecting it in the preceding chapter, and in chap. cli.
[ [24] The eyeball moving up and down to look at the hand, describes a part of a circle, from every point of which it sees it in an infinite variety of aspects. The hand also is moveable ad infinitum (for it can go round the whole circle—see chap. lxxxvii.), and consequently shew itself in an infinite variety of aspects, which it is impossible for any memory to retain.
[ [25] See chap. xx. clv.
[ [26] About thirteen yards of our measure, the Florentine braccia, or cubit, by which the author measures, being 1 foot 10 inches 7-8ths English measure.
[ [27] See chap. cxxi. and cccv.
[ [28] It is supposed that the figures are to appear of the natural size, and not bigger. In that case, the measure of the first, to be of the exact dimension, should have its feet resting upon the bottom line; but as you remove it from that, it should diminish.
No allusion is here intended to the distance at which a picture is to be placed from the eye.
[ [29] The author does not mean here to say, that one historical picture cannot be hung over another. It certainly may, because, in viewing each, the spectator is at liberty (especially if they are subjects independent of each other) to shift his place so as to stand at the true point of sight for viewing every one of them; but in covering a wall with a succession of subjects from the same history, the author considers the whole as, in fact, but one picture, divided into compartments, and to be seen at one view, and which cannot therefore admit more than one point of sight. In the former case, the pictures are in fact so many distinct subjects unconnected with each other.
[ [30] See chap. cccxlviii.