Domestic Encyclopædia (1802)/Jack
Although numerous accidents almost daily happen in using the common jacks, for want of a contrivance to prevent the machine from taking a retrograde course, if the weight should, from any circumstance, overbalance the power, no attempts have till lately been made, to protect the workmen on such occasions. In order, therefore, to supply this deficiency in mechanics, as far as our opportunities will admit, we offer the annexed cut to the consideration of those readers who are not yet acquainted with the improvement it represents.
This machine was, in the year 1794, presented to the Society for the Encouragement of Arts, &c. by Mr. Mocock, of Southwark, for which he was rewarded with a premium of 20 guineas.
Description of the Cut of Mr. Mocock's Improved Machine for raising large weights.
A A, are the double handles of the winch.
B, represents the large toothed wheel, in which the pinion on the axis C works.
D, a ratchet-wheel.
E, the click, or pall, which falls into the teeth of the ratchet, and thus prevents the machine from running back, in case the weight should at any time overcome the power.
F, the rack, as appears in jacks of the common construction.
From a comparison of Mr. Mocock's jack with those in common use, the former differs from the latter only in one respect; namely, that, in the improved machine, a pall, or chick, and ratchet, are applied in such a manner as to stop the machine in the case above mentioned, and thus to prevent those melancholy accidents which frequently occur, especially on board of ships engaged in action; when, from inattention, or neglect in fixing the hooks, or from any other cause, the common jacks fail: and, as the difference in its mechanism is not material, the improvement may be easily applied to the instruments already manufactured.