350 



NA JURE 



[February 8, 1894 



conclude that there is a distant dark body around which the 

 bright star and the dark companion producing echpses revolve 

 in a period of 130 years (Nature, vol. xlv. p. 446). This con- 

 clusion has been greatly strengthened by recent investigation by 

 Mr. Searle, of the relative places of Algol and comparison stars 

 from observations made with the meridian circle at Harvard 

 College [Annals, vol. xxix. 1S93). The right ascension of the 

 star appears to be increasing in general conformity with 

 Chandler's prediction. 



THE INSTITUTION OF MECHANICAL 

 ENGINEERS. 



THE forty-seventh annual general meeting of the Institution 

 of Mechanical Engineers was held on the evenings of 

 Thursday and Friday of last week, in the theatre of the Institu- 

 tion of Civil Engineers. There were two papers down for 

 reading, as follows : — 



" Research Committee on Marine Engine Trials. Abstract 

 of results and experiments on six steamers, and conclusions 

 drawn therefrom in regard to the efficiency of marine engines 

 and boilers," by Prof. T. Hudson Beare. 



"Description of the Grafton High Speed Steam Engine," 

 by Edward W. Anderson, of Erith. 



The reading and discussion of Prof. Beare's paper, together 

 with the introductory proceedings, occupied both evenings, so 

 Mr. Anderson's paper had to be adjourned until next meeting. 



Upon the members assembling on Thursday evening, the ist 

 inst., the President, Dr. William Anderson, took the chair. Mr. 

 Bache, the secretary, then read the annual report of the council, 

 by which it appeared that the Institution continues to flourish, the i 

 income and membership having increased during the past year. 

 After the reading of the report Dr. Anderson vacated the chair, 

 his term of office of two year? having expired, and the new ' 

 President, Prof. Alexander B. W. Kennedy, F.R.S., was duly 

 installed. After the usual votes of thanks, and a few compli- 

 mentary speeches, the reading of Prof. Beare's paper was pro- 

 ceeded with. 



As our readers are aware, the Research Committee on marine 

 engine trials of this Instiiution has been for some time past en- 

 gaged in making trials with different steam vessels. The 

 reports of the committee on these trials have already been re- 

 ferred to in our accounts of former meetings of the Institution 

 at which they have been read. Six vessels have been experi- 

 mented upon altogether since the committee was formed. 

 These ships have consisted of channel passenger vessels and 

 cargo boats, the committee not having had yet an opportunity 

 of experimenting upon an important ship of the ocean liner 

 type. 



The labours of the committee have been brought to a con- 

 clusion, for the present at any rate ; and the paper of Prof. 

 Hudson Beare was intended to give a summary of the results, 

 and afford a basis of discussion thereupon. We are at a loss 

 how to condense within the compass of space at our disposal 

 the mass of data dealt with by the author of the paper. 

 Perhaps the most lasting impression on one's mind, after going 

 through the subject, is that no general conclusions, that can be 

 compactly expressed, are to be drawn from the trials. 

 The conditions of work required from marine engines 

 in ships of different classes are so various that what is 

 paramount virtue in one case becomes an unnecessary refine- 

 ment in another. Thus in the cargo boats the first consider- 

 ation is economy in fuel, to which nearly every other feature in 

 the machinery is usually saciificed. In order to carry cargo at 

 a rate sufficiently low to enable the shipowner to compete, the 

 coal bill must be light, and therefore we find in these vessels 

 boilers lightly worked and speeds low. On the other hand, 

 vessels that have to convey passengers must be speedy, and 

 general economy has to be sacrificed to this end, the 

 model of the vessels themselves being formed with the same 

 purpose in view. Perhaps we cannot do better than quote some 

 of the elements of design of the machinery, and some of the re- 

 sults attained during llie trials, in order to illustrate these leading 

 facts. We will take two of the ships tried — the loiia, a large 

 cargo boat, and the Ville de Doj<vres, a paddle boat carrying 

 mails and passengers between Dover and Ostend. The lona 

 is 275 feet long, 37.3 feet wide, 27 feet 75 inches draught, and 

 4430 tons displacement. Her speed on trial was 8 '6 knots. The 

 Ville de Dotivres is 271 feet long, 29 feet wide, 9 feet draught, 



and 1090 tons displacement. On her trial she made I7'i 

 knots. It will be seen, therefore, that the cargo boat is con- 

 siderably over four times the displacement, and travels at about 

 one-half the speed of the mail boat. As both craft are ap- 

 proximately the same length, the additional size and weight- 

 carrying capacity of the lona is made up by her greater beam, 

 and also by her fuller ends. The engines of the lona are of the 

 three-stage compound, popularly, but erroneously, known as 

 triple expansion engines. As a matter of fact the lonas 

 engines are 19-expansion, the steam being expanded nineteen 

 times in passing through the three cylinders. The Ville de 

 Douvres has ordinary two-cylinder compound engines, 

 in which the steam is expanded but 57 times. The horse- 

 power required to drive the 4430 tons of the bluff-ended 

 lona through the water was but 645 '4 indicated, whilst 

 the Ville de Douvres, modelled for speed, required 2977 

 indicated horse-power to enable her to get her 17 knots. Sup- 

 posing each unit of power to be obtained in both ships at an 

 equal expenditure of fuel, the figures quoted will show the 

 price that has to be paid for speed ; but there is a further item 

 to the debit side of the coal bill in the case of the fast ship. 

 In order to get high speed it is very desirable, indeed neces- 

 sary, that machinery should be light, and light machinery, other 

 things being equal, means a low figure of merit in regard to 

 fuel economy. The lona works, as stated, with 19 ex- 

 pansions, her boiler pressure being 165 lbs. above 

 atmosphere ; whilst the Ville dc Douvres has boilers 

 pressed only to 105 lbs. The result of this greater expansion 

 of steam on the part of the cargo boat's engines, and the easy 

 way in which her boilers are worked, enables each unit of power 

 to be obtained on a consumption of i '46 lbs. of coal per hour ; 

 whilst the Ville dc Douvres required 2 '32 lbs. of coal for each 

 indicated horse-power exerted for an hour. 



It is easy to see from these figures, which are fairly repre- 

 sentative, that economy and speed cannot go hand in hand ; the 

 owner must select whether he would rather travel cheaply (in 

 fuel) or quickly. 



Pursuing the investigation of this branch of the subject, we 

 find that the total weight of the machinery of the lona 

 is 202 tons, which gives 3 'I units of power per ton weight of 

 machinery; whilst the total weight of the machinery of the ]'ille 

 de Douvres was 361 tons, equal to 82 units of power per ton 

 weight of machinery. With regard to space occupied, the 

 engines of the two ships are not comparable, being paddle and 

 screw engines respectively : but in boilers we find that the net 

 volume required for each indicated horse-power with the lona 

 was 4'I5 cubic feet, and with the Ville de Douvres 2*09 cubic 

 feet ; thus showing that space as well as weight may be 

 gained by the sacrifice of fuel economy. In the discus- 

 sion which followed the reading of the paper, Mr. Jeremiah 

 Head, of Middlesborough, gave some interesting figures in regard 

 to those cargo steamers generally known as ''ocean tramps." 

 He stated that the s.s. Westoe, a vessel of this class, had carried 

 3500 tons dead weight at a speed of 9 knots, the fuel burnt being 

 at the rate of "64 oz. per ton per nautical mile, or about one five- 

 hundredth of a penny. Another ship, the Oscar II. of 4600 

 tons dead weight capacity, required a consumption of half an 

 ounce of coal per ton per mile. Still another vessel steaming 

 at 8 '9 knots showed a similar fuel economy. The figures are 

 striking, and easily remembered : half an ounce of coal for each 

 ton carried one nautical mile. 



The boilers of both the Io)ta and the Ville de Dottvres are of 

 a similar type, being the ordinary return tube marine boiler, but 

 the proportions are somewhat different. Thus in the lona the 

 proportion of total heating surface to grate surface is 75 '2 

 percent; in the Ville de Douvres it is but 31*1 per cent. 

 This large extension of the heating surface means both 

 a heavier and more bulky boiler, as has been shown ; but 

 in the cargo boat this sacrifice of weight and space can be 

 profitably made in order that the fullest amount of heat from 

 the products of combustion may be absorbed by the water in the 

 boiler. In the ]lUc de Douvres this heat is allowed to pass oft 

 by the chimney. If we turn to the record of funnel temperatures 

 we find this fact borne out, the escaping gases in the 

 lona being 452° F. and in the Ville de Douvres 910" F., as 

 far as could be ascertained. The coal consumed on a 

 given area of grate in the two vessels does not var}' 

 greatly, it being 22-4 lbs. per hour in the lona, and 31 '3 lbs. per 

 hour in the Ville de Douvres. The different proportions of 

 grate to heating surface in the two ships will, however, be 



NO. 1267, VOL. 49] 



