It must be admitted that this press provides for the greatest possible economy of time, and for the largest output, for the capital employed, which can be attained. The rams and the men are constantly in action, and not a single moment is lost. For filling each box 78 seconds are allowed, and there is ample time for the preliminary lashing.
[Illustration: COMPOUND HYDRAULIC PRESS. FIGS. 5 and 6.]
Figs. 5 and 6 show a modification of this press, designed to turn out sixty bales per hour. It has only one set of long-stroke rams, with three revolvers. The bale receives its preliminary lashing while in the position, B (Fig. 6). Fifty-three seconds are available for filling the box, and the same time for the preliminary lashing. It is found, however, that three-quarters of a minute is sufficient for the complete hooping of a bale.
[Illustration: COMPOUND HYDRAULIC PRESS. FIGS. 7 and 8.]
Figs. 7 and 8 show a similar press intended for jute pressing. This has only one box, which is fixed, as the material has to be packed in an orderly manner. Its speed is sixty bales an hour.--_Engineering._
JET PROPELLERS.--HYDRAULIC PROPULSION OF VESSELS.
Certain mechanical devices appear to exercise a remarkable influence on some minds, and engineers are blamed for not adopting them, in no very measured terms in some cases. It is not in any way necessary that these devices should have been invented by the men who advocate their adoption, in order to secure that advocacy. The intrinsic attractions of the scheme suffice to evoke eulogy; and engineers sometimes find it very difficult to make those who believe in such devices understand that there are valid reasons standing in the way of their adoption. One such device is hydraulic propulsion. A correspondent in a recent impression suggested its immediate and extended use in yachts at all events, and we willingly published his letter, because the system does no doubt lend itself very freely to adoption for a particular class of yachts, namely, those provided with auxiliary power only. But because this is the case it must not be assumed that the jet propeller is better than screw or paddle-wheel propulsion; and it is just as well, before, correspondence extends further, that we should explain why and in what way it is not satisfactory. The arguments to be urged in favor of hydraulic propulsion are many and cogent; but it will not fail to strike our readers, we think, that all these arguments refer, not to the efficiency of the system, but to its convenience. A ship with a hydraulic propeller can sail without let or hindrance; a powerful pump is provided, which will deal with an enormous leak, and so on. If all the good things which hydraulic propulsion promises could be had combined with a fair efficiency, then the days of the screw propeller and the paddle wheel would be numbered; but the efficiency of the hydraulic propeller is very low, and we hope to make the reason why it is low intelligible to readers who are ignorant of mathematics. Those who are not ignorant of them will find no difficulty in applying them to what we have to say, and arriving at similar conclusions in a different way.