a trial with a great number of ships. He wished to show how the actual result thus obtained with the ship corresponded with that indicated by her model. The curve of resistance for the ship, as obtained by the dynamometer, was a curve like the curve AA shown on the diagram. The curve of resistance obtained by the experiments with the model is shown by the curve BB. The model was tried with all the changes of trim and of immersion that the ship had gone through, and it was found, in every instance, that the A A, curve of ship's actual resistance. B B, curve deduced from model for ship if with skin clean painted. C C, curve of ship's skin friction if with surface clean painted. D D, curve of ship's skin friction if with one-fourth part coated with calico over the paint. resistances exhibited by the ship with varied trim and of immersion were reproduced, under the same variations of trim and immersion with the model, almost exactly, but with fairer curves. The dynamometrical results obtained with the ship, though slightly irregular, because it was difficult to get the exact speeds, yielded fair average curves possessing characteristic differences; for instance, they showed that at a high speed the ship did better when trimmed by the stern, and that than when trimmed by the head. were reproduced by the model. at a low speed she did better All those characteristic results The curves, though much alike, implied by their slight difference that, judging by the model, the ship ought to have made rather less resistance than she did, and prima facie, it might be thought that that was evidence of some incorrectness in the indications given by the model. The interpretation of the descrepancy, however, was the following: a very large proportion of the total resistance, whether of ship or model, consists of surface friction, and is measurable in each case by the area of immersed skin, the quality of its surface, and the speed; and an extensive series of experiments had therefore been conducted to determine the co-efficients of resistance for surfaces of various qualities. This series, however, did not include old rough copper, such as that of the ship. The ship's resistance was, in the first instance, calculated on the supposition that the quality of the surface was equivalent to that of smooth paint, and it was the resistance thus calculated that fell short of the truth. It was probable that the rough copper had a more resistent surface; and at all events the difference would have been exactly obliterated if it had been assumed that a strip of ordinary unbleached calico had covered one-fourth part of the surface of the paint. On these grounds he ventured to state that the experiments with models gave a correct measure of ship's resistance, and that in virtue of that measure it was possible to determine how much nett HP. a given ship should require at a given speed, and from numerous comparisons between this and the actual power required, to state that, in a general way, an amount of only from 37 to 40 per cent. of work put into the engine of a screw ship was actually realised. The moral which he desired to draw was the great importance of separating, as far as possible, the expenditure of power into its constituent elements. The Admiralty had instructed him to work out a design for a dynamometer which might be substituted for the screw at the end of a screw shaft to measure exactly the power given out at that point by the engine; and he had succeeded in contriving one somewhat of the nature of a turbine, which, tested by a couple of good-sized models of different dimensions, justified him in the belief that a circular drum or casing about 5 feet 6 inches in diameter and 2 feet 6 inches in length along the screw shaft might contain a turbine, which would take up 3,000 HP. when rotated at about 90 revolutions. He was expecting an order from the Admiralty to get such an instrument made, and in that case the apparatus would be applied and made to record the actual power delivered at the screw end of the shaft by the working engine. Mr. LOFTUS PERKINS said that engines of his design were now working with steam at from 350 to 400 lbs. pressure in tubular boilers (Fig. 3), which appeared to have a long life. They were FIG. 3. igga worked with distilled drinking water or rain water. The samples exhibited were those which the Admiralty Boiler Committee had cut out of boilers worked in that manner for eighteen years; it would be seen that they had not deteriorated. It had been stated by the Author of the Paper that jacketing was of no use; but it had been found that the greater the expansion the more necessary it was to provide the cylinders with jackets. Engines with low-pressure cylinders would stand the jacketing with highpressure steam, 450°, without injury, and the economy was increased by keeping it at that temperature. In working with those high temperatures it had been found necessary to get rid of grease and oil, and a metal had been discovered which required no lubrication. In the course of six months a number of such engines would be at work, so that their capabilities at sea could be ascertained. It had been objected that rough sea usage would injure them, but he did not believe that long voyages would give any trouble. The most troublesome voyages to marine engines were the short ones, and the engines that suffered most were those that were worked on rivers. The expense of keeping in order the engines of passenger ships on the Tyne was equal to the whole remaining expense of maintenance. A boiler worked at sea was fired perhaps once in thirty or forty days, and did not suffer from expansion and contraction. The boilers that suffered most were those fired up twice or three times a day. Mr. JOHN DIXON regretted that the Author had but little hope of future economy in the consumption of fuel. It was true that the consumption had been reduced from 6 to 4, 3, 21, and (in some exceptional cases) to 2 lbs. per indicated HP. per hour. But heat and mechanical force were synonymous terms, and it was well known that 1 lb. of coal ought to produce much more power than was realised from it. Theoretically 1 HP. ought to be produced with lb. of coal, and though that result might not be attained, he thought the consumption might be reduced in a material degree. He did not agree with the Author in thinking that any further saving must lie in the reduction of wages. Engineering talent and the extension of the naval service had produced. an increased demand for luxuries, and hence wages must inevitably continue to advance. Wages, however, might be materially economised by the use of steam for a great part of the somewhat laborious work on shipboard. The Americans had gone far ahead in that direction by the use of donkey engines and other appliances for economising labour. He could see no reason why steam should not be applied in steering, and also in the stoke-hole, in the trimming of the coal and the like. With regard to the attacks that had been made upon the Board of Trade, he thought that those who attacked any public department ought to suggest a remedy for the evils of which they complained. He also thought that a public department like the Board of Trade might do something towards establishing new standards that would be useful to engineers. How many members present could tell what a nominal horse-power was? He was sure he could not. The Author had expressed regret that the steam trade of England had not been very remunerative; but seeing the extent to which the leading firms had increased their steam shipping, and the extent to which the steam shipping of England had been augmented during the last twenty years, it was surely taxing the credulity of the Institution to say that the trade had been a bad one. Captain BEDFORD PIM, R.N., M.P., said the mercantile marine of the country now numbered some twenty-five thousand ships, of which not five thousand were steamers, showing, he thought, that the Author was mistaken in stating that steamers were entirely superseding sailing ships. Having been a great many years at sea, and having seen a great deal of the mercantile marine and the navy, he had no hesitation in saying that the mercantile marine was even of more importance to the country than the Navy itself. Two-thirds of the food of the country were imported from abroad; in fact, an addition of 40,000 tons of shipping was required every year, due alone to the necessity of supplying the new mouths, which increased at the rate of two hundred and sixty thousand per annum, the metropolitan area alone adding to the population about thirty-five thousand souls a year; hence the importance of seeing that the mercantile marine was efficient, not only in ships and engines, but in men, most of whom he was sorry to say were foreigners. He held in his hand a model of the long steamship of the present day, but only nine times her beam for length, whereas ten and eleven times were common. It must be evident to any one who had been at sea what would be the fate of such a vessel if an accident happened to her machinery, and she fell into the trough of a sea in a gale of wind. He maintained that she must inevitably go to the bottom. He also exhibited a model of a ship of the same tonnage, but of proper proportions, four times her beam for length. The long vessel was, no doubt, a fine one for the shipbuilder and the naval architect, but it was a bad one for the shipowner, requiring one-third more iron and materials and heavier scantling. It required also more repairs |