Still, with all these advantages gained, its operations were restricted, by reason of the constant and unremitting attention required from the person employed to work it ; for the most unremitting care fell very short of what was demanded fur the perfect development of its power. When, for instance, the attendant opened the steam cock, he was obliged to watch the ascent of the piston, and at the instant of its elevation to the proper height, it was to be again quickly shut, and at the same moment the injection cock was to be opened; if the one did not follow the other, there resulted a great loss of vapour or of effect ; and this difficulty was further increased by the irregular production of the steam itself, from the varying intensity of the heat of the furnace. After the injection had condensed the steam, and the piston was at liberty to descend, if the communi cation between the boiler and cylinder were not opened at the precise instant, when it had reached the limit of its downward movement, the immense weight on the piston forcing it into the void with a great velocity, would shake the apparatus to pieces. All this precision, too, was required from a mercenary attendant fourteen times every minute, at a hazard of the total destruction of the apwatus.
If cWms to the glory of first suggestion, or of original invention, are to be rigorously insisted upon, the name of Humphrey Potter must not be omitted. We are informed on the authority of Dr. Desaguliers, (and the statement has never been invalidated,) that "it was usual to work with a buoy in the cylinder, enclosed in a pipe, which buoy rose when the steam was strong and opened the injection pipe, and made a stroke, whereby they were only able, from this imperfect mechanism, to make six or eight strokes in a minute, till a boy named Humphrey Potter, who attended the engine, added (what he called a seaman), a catch, that the beam or lever always opened, and then it would go fifteen or sixteen strokes in a minute." To wog, is a verb, found in certain vocabularies throughout the north of England, implying to sculk ; and this young gentleman, impelled by a love of idleness, or play, common to boyhood, and having his wits about him, after due meditation, devised this contrivance. by which so important an improvement was effected, and himself allowed the means of " scogging" for his own diversion.
Up to this period it may be supposed that the completion of a motive power had exclusively engaged the attention of scientific inquirers upon the steam engine, the auxiliary details of mechanism to afford facilities of action being passed over as matters of less importance ; but it is obvious that the device of this boy, by which the atmospheric engine was nearly rtndered a self-acting one, must needs have provoked instant attention.
To prevent the accidents which arose from the neglect of the attendant, and the frequent derangement of the engine consequent thereupon, means were now there fore contrived to make it less dependant upon his attention. Strings were applied to connect the handles of the cock with the beam, so that they should be turned whenever it was in certain positions; these, again, were gradually changed and improved into detente and catches of different forms ; and at length Mr. Hemar BEIGHTON of Newcastle-upon-Tyne, (a mathematician and engineer,) con structed ;hat he called the "hand gear," whereby motion was given to all the cocks and levers by a rod from the beam operating upon a series of tappets. An engine with these improvements was erected in 1718, and was the first in which a graduated lever, or a steel-yard safety-valve, was employed.
Mr. Beighton, in the course of the previous year, had published a table of the proportions of the cylinders of engines to the pumps, when drawing water at different depths, from 15 to 100 yards, in different quantities from 48 to 480 hogs heads per hour. As this table has been verified by practice since that time, and the particulars therein contained are of deep importance to those who are practically concerned, it will be found transcribed in an abridged form in the following page. The measures are in English ale gallons, (each containing 282 cubic inches,) and the allowance made for friction, &c. reduces the atmo spheric pressure from 141 lbs. to 8 lbs. to the inch or the base of the cylinder To use this table, suppose it was required to draw 150 hogsheads per hour, at 90 yards deep : in the seventh column seek the nearest number, viz. 149 hogsheads, and against it, in the first column, is found a pump of seven-inch bore ; then, under 90, the depth on the right hand in the same line is given the diameter of the cylinder (27 inches) fit for that purpose, and so for any other.
About three year after the publication of these tables, namely, in 1720, LEUPOLD, the author of the Theatrean Machination Hydraulicarten, constructed the first high-pressure engine. With much modesty he ascribes the invention to Pepin, on account of his having furnished the idea of applying the expansive force of steam for the purpose of raising water ; and also because he took the construction of the four-way cock to communicate alternately with two cylinders, from Papin's air-machine. The merit of first contrivance, however, must unquestionably be conceded to Leupold. His apparatus is unrivalled for simplicity, and exhibits with great clearness the method of applying steam in alternate action. The subjoined figure (which nearly resembles that given by Leupold) and explanation will sufficiently illustrate the principle.