While the last few years have seen great advances made in the designs of steamships and of their engines, little or nothing has been done in the way of improving the screw propeller. As a general rule it would appear to be taken for granted that no radical improvement could be made in the form of the propeller, although various metals have been introduced in its manufacture with the view of increasing its efficiency. For sea-going steamers, however, the shape remains the same, the variation chiefly relating to the number of blades employed. A striking departure from ordinary practice, however, has of late been made by Mr. B. Dickinson, who has invented a screw propeller which, on practical trial, has given an efficiency far in advance of the ordinary screw. This new propeller we illustrate here in Figs. C and D, while Fig. A shows an ordinary propeller. The Dickinson propeller illustrated has six blades, giving a surface of 30 square feet; it is right handed, and has pitch of 15 ft. and a diameter of 10 ft. 6 in. The ordinary screw propeller shown at Fig. A is right handed and two bladed, with a pitch at the boss of 13 ft. 6 in. and at the tip of 15 ft. It has a diameter of 10 ft. 9 in. and 32 square ft. of surface.

The projected area looking forward is 22 square ft. and the projected area looking athwartship 22.84 square feet. The most graphic way of illustrating the principle of Mr. Dickinson's propeller is to take a two bladed propeller of the ordinary type as shown at Fig. A in the annexed cuts, and divide into three sections as in Fig. B, then move section No. 1 to the line position on the shaft of No. 3, and No. 3 to that of No. 1, No. 2 remaining stationary. The effect of this interchange will be that (having regard to the circle of rotation) No. 3, the rearmost section, will rotate in advance of No. 2, and No. 2 in advance of No. 1 (see Fig. C). By this arrangement the water operated on escapes freely astern from every blade - that from No. 1 passing in the wake of No. 2, while that from Nos. 2 and 1 passes in the wake of No. 3. Fig. D represents the blades with a wider spread as practically used. The advantages claimed by Mr. Dickinson for his propeller, and which are sufficiently important to be given in detail, are:

1. That the blades of each section, when the vessel is in motion, necessarily cut solid, undisturbed water, each blade operating upon precisely the same quantity of water as an individual broad blade would do, though, of course, it parts with it in one-third of the time.

2. That each sectional blade exerts the equivalent efficiency of the first or entering third portion of the breadth of an ordinary propeller blade, and that consequently the combined sections have greater effective power. It is now regarded by experts as an ascertained fact that the after or trailing portion of the broad blade is relatively non-effective as compared with the forward or entering portion.

3. When three blades are fitted, the spent water from No. 2 being delivered immediately in the wake of No. 3, and that from No. 1 in the wake of No. 2, has the effect of destroying or reducing to a minimum the back draught of sections Nos. 2 and 3, No. 1 alone being subject to this drawback. This is of greater importance than might at first thought appear, as in cases where there are three or four blades revolving in one plane, the water is drawn after the retreating blade, lessening the resistance to the face of the advancing one.

4. That by the subdivision of the blades, as arranged spirally, the water passing through within the radius of the propeller has its resisting capacity more thoroughly worked out than is possible with any propeller whose blades are all on the same plane. This view is confirmed by the visibly increased rotation of the water in the wake of the vessel.

5. That by broadening the blades or increasing the number of sections, the diameter of the propeller may be proportionately diminished without the sacrifice of engine power. This is often desirable with vessels of light draught, the complete immersion of the screw being at all times necessary to avoid waste of power.

6. The propeller being made and fitted on the shaft in sections, all that is necessary in case of accident is to replace the broken section. This in many cases could be done afloat.

7. The blades being arranged to take their water at different planes, there is the greater certainty of one or other of the sections operating upon what is termed the water of friction. This is considered an advantage.

8. Where it is desirable, the blades of the different sections can be made of varying breadth or pitch.

9. The principle of division into two or more sections applies equally to two, three, or four bladed ordinary propellers.

10. The adoption of this principle does not entail any alteration or enlargement of the screw space or bay as usually provided.

11. As a consequence of the freedom and rapidity with which the water operated upon escapes from the narrow blades, the depression at the stern of the vessel caused by the action of the ordinary propeller is greatly reduced.

12. The vibration caused by this propeller is so slight as to be hardly noticeable, thereby effecting a saving in the wear and tear of the engine and machinery. This may also be a consideration in promoting the comfort of passengers.

From a practical and working point of view we take Mr. Dickinson's chief claims to be, in the first place, the yielding of a greater speed per power employed, or an economy in obtaining an equal speed; in the second, increased, rapidity in maneuvering and stopping a vessel; and in the third, a reduction of vibration. In order to put these claims to a practical and reliable comparative test, Messrs. Weatherley, Mead & Hussey, of Saint Dunstan's Hill, London, placed at the inventor's disposal two of their new steamers, the Herongate and the Belle of Dunkerque. These are in every respect sister boats, and were built in 1887 by Messrs. Short Brothers, and engined by Mr. John Dickinson, of Sunderland. The Herongate was fitted about four months ago with the largest propeller yet made on Mr. B. Dickinson's principle, the Belle of Dunkerque having an ordinary four-bladed propeller of the latest improved type. Every precaution was taken to place the two vessels on the same footing for the purpose of a comparative test, which was recently carried out.

Both vessels previously to the trial were placed on the gridiron, cleaned and painted, their boilers opened out and scaled, their steam gauges independently tested, and both vessels loaded with a similar cargo of pitch, the only difference being that the Herongate carried 11 tons more dead weight and had one inch more mean draught than the Belle of Dunkerque, while the former had been running continuously for nine months against the latter's two and a half months. On the day of the trial the vessels were lying in the Lower Hope reach, and it was decided to run them over the measured mile there with equal pressure of steam. The order of running having been arranged, the Herongate got under way first, the Belle of Dunkerque following over the same course. Steaming down against tide, the Herongate is said to have come round with remarkable ease and rapidity, and in turning on either helm, whether with or against tide, to have shown a decided advantage. Equally manifest, it is stated, was the superiority shown in bringing up the vessel by reversing, when running at full speed, thus confirming the very favorable reports previously received by the owners from their captains since the Dickinson propeller was fitted to the Herongate. Those who were on board her state that the vibration was scarcely noticeable.

From a statement submitted to us it is clear that the Herongate had the turn of the scale against her in dead weight and draught, vacuum, and diagrams taken, but notwithstanding (making allowance for one faulty run due to the variations in tide) she appears to have more than held her own in the matter of speed, with a saving of 4½ and 3¼ revolutions per minute at 140 lb. and 160 lb. steam pressure respectively. This is further confirmed by the results of a run made after the experiments were concluded, the two vessels being placed in line, and fairly started for a half hour's run over the flood with 150 lb. steam pressure. At the expiration of that time the Herongate was judged to be leading by at least half a length, her revolutions being 76, as against 80 in the Belle of Dunkerque. It was agreed by all present at these trials that the propeller had realized in full the three main working advantages claimed for it. This being the first Dickinson propeller fitted to a sea-going vessel of this size, it is quite within the limits of possibility that the present results may be improved upon in further practice.

In any case we can but regard this propeller as a distinct and original departure in marine propulsion, and we congratulate Mr. Dickinson on his present success and promising future. Messrs. Weatherley, Mead & Hussey also deserve credit for their discernment, and for the spirited manner in which they have taken up Mr. Dickinson's ingenious invention. We understand that they are so satisfied with the results that they intend having one of their larger ocean-going steamers fitted with the Dickinson propeller. - Iron.