OF
AN HYDRAULIC LAMP
For the Table.
I call this an Hydraulic Lamp, to distinguish it from the Hydrostatic Lamps, commonly so named: and I think the distinction proper, because this Machine acts in a different manner. It’s principle will be seen in a moment, by turning to the [5th figure], of [Plate 33]. If, there, we pour oil (or any liquid) into the bent tube A D G at A, the first effect will be to raise it to C, in the rising branch B C; and from C it will trickle down the branch C D, leaving the air, there, to occupy it’s own place. Continuing to pour, slowly, more oil into A the trickling oil in C D will ultimately fill the rising tube E D, expelling the air before it; and, now, the weight to balance the column in A B will be both the columns B C and E D; whence, of course, that column will rise as far above C as C is above B; that is, half-way between C and A. Here, there would be a small deduction to be made, if the height B C were considerable; but, as it is only supposed to be about a foot, the compression of the air in C D, &c., (being about 1⁄3 of a foot or 1⁄90 of an atmosphere) may be neglected. Continuing, then, to pour oil into A, we shall again fill, not the descending tube E F, but the rising tube F G; whose column will thus be to be added to those B C and E D; so that now the column A B will rise to A, and there abide, as long as the mouth G is kept full, or nearly so.
The above is the principle of the Lamp announced in the title; whose effect depends, then, on the number of bends made in the tube A D G, which number (whatever be the form) it would be well to make rather greater than smaller, as the height B C, &c., might be so much the less, compared with the whole height of the column A B; by which means, also, a smaller difference in the level of the column below, would return the oil necessary for the consumption of the wick above.
I have given this idea what I think a better form in [fig. 6]. Instead of the bent tube A G, of [fig. 5], this form supposes a series of air-tight cups, embracing each other; one half of them with their mouths opening upwards, and the other half with theirs opening downwards. They are shewn, by a section only, in this [fig. 6]; where a b c, c b a, present the under cups, forming one piece with the outer surface of the bottom vessel d a c, c a e: and, while speaking of this part of the Machine, I would just indicate it’s cover d e f g put on like the lid of a snuff-box, and carrying a case or tube f g, the use of which will be mentioned in a moment. To proceed, then, the upper vessel is shewn by the edges of it’s cups seen immediately over the figures 1 2 3, 4 5 6, placed between the letters a b c, &c.—These inverted cups make also one body with the moveable cover shewn between d and e, and to which is soldered the tube h i—which, sliding in the case f g, keeps this inverted vessel steady. Where note: that there is an inner tube soldered into the tube h i, through which alone the oil rises, and which can hardly be made too small, since it has only to supply the consumption of a lamp—namely, a few ounces of oil in a whole evening. We may, finally, take notice of the weight placed under f g, upon the said inverted vessel, and which helps to counterpoise the oil in the rising tube h i; which tube, as before observed, may be as many times higher than the distance a d or e a, as there are rising columns between the cups a b c and those 1 2 3, &c.