In [Plate 25] [fig. 1], A B are two screws, perfectly like those used in exhausting watery foundations; and named of Archimedes. They are placed perpendicularly in the frame C D, so as to turn in the cross bars a b, c d, fixed horizontally on the main shaft E F of the Machine. At the bottom of this shaft, E F, (which turns in a step on the sill G D) is a low cylindrical vessel, shewn by a section only at e f, which dips into the under water nearly to the brim. It is used to carry, in proper steps, the centres of the screws A B, and, being pierced with many holes, to feed them amply, without exposing their motion to any resistance from the stagnant water. These cylinders A B are merely indicated as screws by the threads, dotted between h and d and e and g, and their upper mouths are seen near a b, just under the cross piece marked with these letters. These screws then, are turned by the wheels i k, as actuated by the fixed wheel m n, in the same manner as those of the [churn] before described; which in fact, is a corollary from this Machine, but of much later date. To return to the Helico-centrifugal Machine—the screws A B are terminated above by circular plates o p (marked with the same letters in [fig. 2 and 3]) intended to receive the water from the mouths of the screw-threads a b, and carry it on to the plate q q, which insures it’s further progress into the ring canal r s, also shewn by a section only, to prevent confusion in the figure. Now what raises the water in these upright screws, is, it’s own centrifugal force, combined with the revolution of the screws: for while this central force is urging the water outward, the screws are bringing their sloping threads like wedges, against that tendency; and the consequence is, that the water actually rises perpendicularly till it flows over the ledges or rings o p, on the plate q q, and thence into the ring canal r s, from which it is conveyed to any place desired.
If this Machine is well made and proportioned, I think it is one of the best that can be used, to do much work by a given power: It gives no shock to the water; which, when once in motion, continues to rise, and escapes when arrived at it’s proper height: and, being spread over a large surface, no part of it is raised higher than enough. The perfection of the Machine depends on a due relation between the centrifugal force, and the sine of the angle, which the threads of the screw make with the horizon; and this may be modified by the diameter of the wheels i k, as compared with that of the screws A B.
The [figures 2 and 3], are two views of the upper part of the Machine. They shew, and mark with the same letters, the cross bar a b, the inside of the screws, and the circular plates o p, together with the circular conducting plate of which q q, [fig. 1], is the section. [Fig. 3] shews the fixed wheel m n, the two screw-wheels i k, the cross piece a b, and under them the plates o p of the 1st. and 2d. figure.
One other object claims our attention: The threads of the screws (whether more or less numerous) should each be furnished with a valve at bottom: that the water may not run out when the Machine ceases working.