1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



189 



M. Norman said, that M. Cave had tried a series of experiments on screws 

 of various forms working in cylinders ; and also, he believed, with shrouding 

 on their extremities, and he understood that no advantage had been found to 

 result from such modifications. 



Mr. Cowper presented an instrument, which he had exhibited when the 

 aerial machine was incidentally mentioned ; it consisted of a fan composed 

 of three or more blades, set at a regular curve upon an axis. When this 

 axis was placed vertically in a socket, and a rapid rotary action communi- 

 cated to it, the fan rose in the air to the height of between 100 and 150 feet. 

 On reversing this fan and using the same propelling force, it would not rise at 

 all. This fact evidently showed that the action of the curved fan upon the 

 air, or of the propeller upon the water, was like that of a screw in a solid, 

 every part of the surface of the blade of a well formed propeller producing 

 its portion of effect. Mr. Cowper directed attention to the contrary effect 

 produced by two fans of similar areas, whose arms were, in the one case, 

 mere planes set at an angle with the axis, and in the other, blades forming part 

 of, and being placed at a given curve around the axis. If it were supposed, 

 that the surface of each blade was divided into a given number of equal 

 parts, when the fan, of the former or angular shape, was set in motion, the 

 first part impinging on the air, communicated a movement to it, and the 

 second and succeeding parts finding no resistance from the disturbed fluid, 

 the body bad no tendency to rise ; but in the latter, or curved shape, the 

 second and succeeding parts, tended to overtake and act upon an undisturbed 

 fluid, and thus had a tendency to rise upon an irregular inclined plane, de- 

 scribed by its gyration through the air. By the law that the resistance in- 

 creased as the square of the velocity, he conceived, that in adapting propel- 

 lers to vessels, their dimensions should be proportioned, not only to the area 

 of the midship section, but also to the speed of the engine. At the same 

 time, the consideration of the form of the blades was very important. In 

 experiments with the revolving fan instrument, he found, that although on 

 all occasions, the same rotative force was applied, a fan with three arms, 

 whose united areas were 3"721 inches, when set at a given angle, did not 

 rise freely ; the same form and area, when set to a proper curve, rose to a 

 very considerable height ; but when a fan of twelve arms, formed from a 

 circle or disc of 28'274 inches area, divided into twelve arms was set in 

 motion, it would not rise at all. With other fans, of intermediate forms, 

 areas, and curves, various results were obtained, which were curious problems 

 for engineers interested in the construction of propellers. 



Mr. Grantham expressed his pleasure at finding his paper bad so much 

 excited the attention of the meeting, and be hoped it would be followed by 

 communications from members who bad devoted more time to the subject ; 

 for instance, the numerous experiments made by Mr. Brunei and Mr. Guppy, 

 before deciding on the use of the screw-propeller for the Great Britain, and 

 those made in the presence of the Government Engineers, Mr. Lloyd and 

 Mr. Murray, on board the Bee, the Rattler, &c., would be very interesting. 

 Mr. Grantham exhibited a diagram of the propeller used on board the 

 JAverpool Screia, figs. 7 and 8 ; composed of four blades with broad shovel ends, 

 fixed at a mean angle of 45°. This form, although very successful in this 

 case, could not, he thought, be recommended for large diameters. The re- 

 sults of his observations induced him to think, that the blades of a propeller 

 should not be more than four feet apart ; he would, therefore, advise the 

 adoption of Ericson's form, and mode of construction, which he considered 

 the best that had hitherto been introduced ; the ring within the arms per- 

 mitted any number of blades to be affixed, and a large area of acting surface, 

 judiciously disposed, could thus be obtamed. He objected to propellers with 

 three arms, cliiefly on account of the small amount of surface obtained. 

 As to the " slip," which Mr. Galloway had so ably commented upon, he was 

 aware that it did exist in all cases, but he was of opinion that the amount 

 was exaggerated ; he had not only made accurate experiments with Massey's 

 log, but being repeatedly in a small boat, which was towed close astern of 

 the Liverpool Screw, be found that there was very slight disturbance of the 

 water, and that there was not any depression behind the blade of the pro- 

 peller on entering the water; this could be easily observed, as a portion of 

 the upper blade was always above the surface. It bad been anticipated that 

 this arrangement would, with so short a vessel as the Liverpool Screw, have 

 caused a constant tendency to bear over in one direction, but not the slightest 

 disturbance of the steering was perceived, and the vessel's course seemed to 

 be quite as straight as it would have been with paddle wheels. Mr. 

 Grantham wished it to be understood, that his object in bringing forward 

 the account of the Liverpool Screw, was not so much to cite that vessel's 

 powers, as to point out the feasibility of working propellers at a slower 

 speed, and that condensing engines could be applied with advantage, avoiding 

 the bands and gearing, which bad hitherto been found so objectionable. 



Mr. Braithwaite was of opinion that where deep immersion was not prac- 

 ticable, two propellers would be preferable, in order to prevent any distur- 

 bance in the steering. Captain Ericson had adopted that plan in boats of 

 light draught. Mr. Braithwaite then presented a drawing of the midship 

 section of the Princeton American frigate, showing the elevation of Ericson's 

 engine on hoard. The vessel was 1C4 feet long, with a breadth of beam of 

 30 feet ; the depth of the hold was 22 feet 6 inches, the draught of water 

 was 17 feet G inches, and the burthen about 700 tons; the propeller was 

 14 feet in diameter, with six blades, and made from 32 to 36 revolutions per 

 minute, at which rate the vessel's speed was stated to be nearly 14 miles per 

 hour. The engines were about 400 horses power; they were of peculiar 

 oustruction, having two steam cyUnders or chests, containing vibrating 



pistons or flaps, with cranks upon the ends of the suspending pivots ; both 

 these were coupled by connecting rods to a main crank on the driving shaft ; 

 the length of these cranks being so proportioned, that their alternate vibra- 

 tions should give a rotary motion to the main crank, and thus act directly 

 upon the propeller, without the intervention of bands or gearing." This 

 principle was tried successfully in the year 1839, by Ericson, on the Thames, 

 in a tufi-hoat named the Robert Stockton, " after the projector, who had suc- 

 ceeded in introducing the system to the American navy, and now commanded 

 the Princeton. The boilers of the Princeton were constructed for burning 

 Anthracite ; the whole of the machinery was so placed as to be out of the 

 reach of shot, and the vessel was ship-rigged, so that by unshipping the 

 screw, she could be rendered as effective as any sailing vessel, with a fair 

 wind, or in case of accident to her machinery. Mr. Braithwaite hoped in a 

 short time to bring before the Institution, an account from Captain Ericson, 

 not only of the Princeton, but of several of the other vessels he had fitted 

 with his engines and propellers, since bis residence in the United States. 

 Figs. 9 and 10, Plate VII. are drawings of Ericson's Screw Propeller. 



Mr. Galloway said, that during the experiments with the Archimedes, a 

 proof had been ehcited that the "following current" had a very considerable 

 effect on the action of the propeller. During one of the trials the vessel 

 was backed astern, when it was found, that the speed of the engine increased 

 three or four revolutions per minute, while the speed of the vessel appeared 

 to have diminished. This experiment was, he contended, conclusive as to 

 the fact that the " slip " was greater than would appear by looking merely 

 at the rate of the vessel compared to that of the screw. He did not, how- 

 ever, think that the "slip" ought to be considerable, with a well-constructed 

 propeller. Increased magnitude in a screw, would have the same effect in 

 creating resistance, as increased magnitude in any other submerged body. 

 The utility of the increasing pitch, however, was involved in, and solely de- 

 pendent on, the amount of "slip" which would be found to be attended 

 with the least disadvantageous results in other respects; and here Mr. Gal- 

 loway would observe that Mr. Cowptr's experiments with the revolving fan 

 instrument confirmed bis view ; for it must be recollected, that there the 

 " slip " was much greater than the rate of ascent; the only condition being 

 thus developed in which the utility of an increasing pitch could be con- 

 tended for. The advantage of turning the propeller by the direct action of 

 the engines, was generally acknowledged. The method of driving it was 

 nearly the only problem remaining for solution, and that difficulty being once 

 overcome, screw-propellers must necessarily, from their vast advantage over 

 paddle wheels, in every respect but that, be universally adopted. 



Mr. Hawkins said, that about the year 1825, Mr. Jacob Perkins adapted 

 to the stern of a canal boat, a propeller of about 25 feet in circumference, 

 which might be described as resembling two sets of windmill vanes, the solid 

 axle of one set revolving within the hollow axle of the other, the two axles 

 being turned in contrary directions, and the dip of the blades being about 

 half their radius. The propulsive force was stated to have been very 

 effective; the experiments, which were put an end to by the breaking of 

 part of the engine, were never renewed, in consequence of disputes among 

 the patentees; but he considered that propeller as the best that had hitherto 

 come under his notice, and he had endeavoured to draw attention to it by. 

 reading an account of it, at the meeting of the British Association at Cork, 

 in 1843. 



Mr. Grantham stated, that in order to test the comparative effect of the 

 expanding pitch, Mr. Woodcroft had adapted to the stern of a vessel, two 

 screws of equal area, one being of a regular, and the other of an expanding 

 pitch ; they were connected by a cross shaft, and were worked by manual 

 power, and it was found that the vessel alv/ays yielded to the impulse of the 

 expanding pitch propeller, and was turned by it from the direct course. 

 With respect to the advantage of a large amount of surface, be bad found 

 that the action of the propeller of the Liverpool Screw, which had been en- 

 larged three times, was decidedly improved by the alterations ; the speed of 

 the engines always remaining the same. 



Mr. Galloway said, that the surface of the propeller of the Liverpool Screw, 

 might probably have been too small at first, and therefore each increase would 

 naturally improve its effective power. The area of the propeller should be 

 in proportion to the body to he moved ; this law was common to screw-pro- 

 pellers and to paddle-wheels. 



The President expressed the gratification he felt at the useful discussion, 

 which bad been raised on so interesting and novel a subject as the screw- 

 propeller, which bad become one of such importance in steam navigation, 

 that the Government had directed the serious attention of their officers to 

 it; and he trusted that the examination of this question, like that of the 

 action of Cornish engines, at the meetings of the Institution, would mate- 

 rially tend to its elucidation. As soon as any new and really useful invention 

 was matured, and brought sufficiently into use, to enable its merits to be 

 calmly discussed, it was one of the main objects of the meetings, to examine 

 it, and he hoped that in a short time a detailed account of the Atmospheric 

 Railway, would be submitted by Mr. Samuda, for the consideration of the 

 Institution. 



OXYDATION OF laON. 



Mr. Perkins stated, that on a recent examination of the Napoleon at Mar- 



5 Vide Mech. Mag., 

 1839, p. 281. 



vol. xxxii., January, 1840, p. 290. 6 Ibid., vol. xxx., January 



