14 24 0 vir 1 Lunation 29 12 44" 3' 6th 21 In leap years, after February, a day and its motion must be added to the time for which the moon's mean distance from the sun is given. But when the mean time of any new or full moon is required in leap year after February, a day must be subtracted from the mean time thereof, as found by the tables. In common years they give the day right. A Table of the Sun's mean Motion from the Christ 1, was the 4007 year The 4008th year yefore the year of before the year of his birth; and is supposed to have been the year of the creation. have 365 days, and the Julian years, 3 of which 4th 366. Complete Sun from node. years. 95 23 53 9 Nov. 10 15 44 5 10 6 12 58 33 Dec. 11 16 53 34 This table agrees with the old stile until the year LECT. XII. A Table of the Sun's mean Motion from the In leap years, after February, add one day and one day's motion to the time at which the sun's mean distance from the ascending node is required. A SUPPLEMENT TO THE PRECEDING LECTURES, BY THE AUTHOR. MECHANICS. The Description of a new and safe Crane, which has four different powers, adapted to different weights.' of a new crane. THE common crane consists only of a large Description wheel and axle; and the rope, by which goods are drawn up from ships, or let down from the quay to them, winds or coils round the axle, as the axle is turned by men walking in the wheel. But, as these engines have nothing Our author received a reward of fifty pounds for the invention of this crane, from the Society for the encouragement of Arts; and a description of it was honoured with a place among the Transactions of the Royal Society of London, see vol. xlv, p. 42.—E», to stop the weight from running down, if any of the men happen to trip or fall in the wheel, the weight descends, and turns the wheel rapidly backward, and tosses the men violently about within it; which has produced melancholy instances, not only of limbs broke, but even of lives lost, by the ill-judged construction of cranes. And besides, they have but one power for all sorts of weights; so that they generally spend as much time in raising a small weight as in raising a great one. These imperfections and dangers induced me to think of a method for remedying them. And for that purpose, I contrived a crane with a proper stop to prevent the danger, and with different powers suited to different weights; so that there might be as little loss of time as possible: and also, that when heavy goods are let down into ships, the descent may be regular and deliberate. This crane has four different powers: and, I believe, it might be built in a room eight feet in width: the gib being on the outside of the room. Three trundles, with different numbers of staves, are applied to the cogs of a horizontal wheel with an upright axle; and the rope that draws up the weight coils round the axle. The wheel has ninety-six cogs, the largest trundle twenty-four staves, the next largest has twelve, and the smallest has six. So that the largest trundle makes four revolutions for one revolution of the wheel: the next makes eight, and the smallest makes sixteen. A winch is occasionally put upon the axis of either of these trundles, for turning it; the trundle being then used that gives a power best suited to the weight: |