FOOTNOTES:
1 More exactly through 16112 feet, or 193 inches.
2 This ratio is that of 31,416 to 10,000 very nearly.
3 Lardner on the Steam-Engine, Steam-Navigation, Roads, and Railways. 8th edition. 1851.
4 From the Greek words tachos speed, and metron measure.
5 Theatrum Machinarum, tom. ii. pl. 36. fig. 3.
6 In a strictly mathematical sense, the path of the point P is a curve, and not a straight line; but in the play given to it in its application to the steam-engine, it moves through a part only of its entire locus, and this part extending equally on each side of a point of inflection, the radius of curvature is infinite, so that in practice the deviation from a straight line, when proper proportions are observed in the rods, is imperceptible.
7 The variation produced in the height of the column of mercury (supposed to be 612 inches high) by an alteration of ± 16° in the temperature will be only ± 1100 of an inch, or in other words, 1100 of an inch will be the total variation from its mean state, by an alteration of 32° in the temperature. It is therefore probable that, in most cases of moderate alteration in the temperature, the centre only of the column of mercury is subject to elevation and depression, whilst the exterior parts remain attached to the sides of the glass vessel. It was with a view to obviate this inconvenience that Henry Browne, Esq. of Portland Place (I believe) first suggested the piece of floating glass.