NA TURE 



S77 



THURSDAY, OCTOBER 20, 1887. 



THE ENCYCLOPEDIA BRITANNICA. 

 The Encydojxedia Britannica. Vol. XXII. Sib— Szo. 



(Edinburgh: A. and C. Black, 1887.) 

 *HE leading mechanical articles in this volume are full 

 of interest to the general reader, and contain all recent 



iformation sought after by the specialist. Captain C. 

 G. Bridges, R.N., contributes a short and concise 



tide on naval signalling. The article is well written, 

 ind contains a large amount of historical information 

 condensed into a small compass. The history of signal- 

 ling is traced from a very early period. In fact, we are 

 told that Polybius described two methods — one proposed 

 by ^neas Tacitus, 300 B.C., and one introduced by him- 

 self, by which any word could be spelled, thus embodying 

 the underlying principle of all recent methods. After an 

 account of signalling by combinations of flags, perfected 

 by different people at different periods, we come to 

 Captain Philip Colomb's flashing system of signalling 

 adopted in the navy in 1867. By means of the Morse 

 alphabet, using long and short flashes of light by night, 

 and blasts of a horn or steam-whistle during a fog, or by 

 waving a flag in day-time, any communication can be 

 made by this system. For short distances the semaphore 

 is now greatly used. This consists of a vertical post 

 with two arms movable in a vertical plane, the changing 

 positions of the arms indicating different letters. 



The article on sounding, by Mr. W. E. Hoyle, is a 

 very short restimi of the subject. The operations in 

 sounding are described, and the gradual improvement in 

 the apparatus used is traced to the present date ; beyond 

 this there is nothing particular to note, and the article 

 might have been extended with advantage. 



The most exhaustive article in the volume is by Prof. 

 J. A. Ewing, on the steam-engine. Prof. Ewing has 

 skilfully condensed into twenty-six pages a large amount 

 of useful information. To commence with, we have a 

 good historical account of the early inventions. Hero, 

 Savery, Papin, and Newcomen have each their place, 

 and receive careful attention at the hands of the author. 

 Watt's inventions are described, and the several forms of 

 his engines are clearly illustrated. 



The compound engine, the engine of to-day, dates from 

 1781, when Jonathan Hornblower patented an arrange- 

 ment of two cylinders of different sizes, the steam being 

 first admitted into the smaller cylinder, then passing into 

 the larger, doing work in each cylinder. Woolf revived 

 this class of engine in 1804, and in 1814 introduced it as 

 a pumping-engine in Cornwall. 



Richard Trevithick shortly afterwards introduced, in 

 Cornwall, a single-cylinder high-pressure engine, which 

 very soon was generally adopted, and became known as 

 the "Cornish" pumping-engine. This engine worked 

 with a comparatively high steam-pressure, and with 

 considerable expansion. The cylinder was placed 

 under one end of an over-head beam, and the 

 pump rods were connected to the other end. The 

 steam was admitted above the piston for a short por- 

 tion of the stroke and then cut off, expanding the re- 

 maining portion, and doing work by lifting the pump 

 Vol. XXXVI.— No. 938. 



rods and their attachments. The space above and 

 below the piston was then put into connexion through 

 the equilibrium valve, and the piston ascended by 

 reason of the weight of the pump rods and gear, and did 

 work in the pumps. The frequency of the stroke was 

 regulated by means of a device called a cataract. This 

 class of engine was used for many years and reached a 

 high state of efficiency ; we are told that the Fowey 

 Consols engine has a consumption of coal of only i| lbs. 

 per horse-power per hour, a result considered exception- 

 ally good even to-day. 



Prof. Ewing treats the steam-engine as a heat-engine 

 in a masterly manner. Nothing of importance has been 

 omitted ; the arrangement of facts being in a carefully 

 condensed form and easily followed. The actual behaviour 

 of steam in the cylinder is demonstrated, and the 

 effects of " wire drawing" and clearance in the cylinder 

 and steam ways are duly explained. He carefully 

 treats the testing of steam-engines ; the best modes of 

 taking indicator-diagrams are given, and points liable to 

 be forgotten are well looked after. The actual testing 

 is explained by means of a numerical example, viz, the 

 trial of a compound beam engine, steam-jacketed, with 

 an intermediate receiver between the cylinders. On 

 compound expansion Prof. Ewing has a great deal to say. 

 The indicator-diagrams illustrating the letterpress are 

 very clear and to the point. 



Next we find a good general description of steam- 

 engines and boilers for stationary, marine, and locomotive 

 purposes. These are well described, and few, if any, im- 

 portant points omitted. Under the head of locomotives 

 we have an account of Mr. F. W. Webb's compound 

 locomotive. This is a three-cylinder engine, having two 

 equal high-pressure cylinders fixed outside the frame, and 

 driving the trailing-wheels by means of two crank-pins at 

 right angles ; a single low-pressure cylinder of suitable 

 dimensions is set under the smoke-box, and is coupled to 

 the driving-wheels by means of a single-throw cranked 

 axle. The two high-pressure cylinders exhaust into the 

 low-pressure valve-chest, and this in its turn exhausts 

 into the atmosphere through the blast-pipe. These 

 engines are doing good service on the London and 

 North-Western Railway, and a considerable saving of 

 fuel is claimed for them over the quantity used by 

 ordinary locomotives working the same traffic. 



Prof. Ewing has, however, omitted to mention Mr. T. 

 W. Worsdell's successful compound locomotive, first 

 tried on the Great Eastern Railway, and now being 

 used on the North- Eastern for passenger and goods 

 traffic. This engine is very little different from the 

 ordinary locomotive, the only difference being that the 

 two cylinders used are of unequal diameters to suit com- 

 pound working. This is probably a special gain because 

 no radical change is made in the general arrangement, 

 and the different parts of the valve motion, &c., come in 

 equally well for the compound as for the ordinary engine. 

 The main feature of the Worsdell engine lies in the 

 starting arrangements. A locomotive must be able to 

 start in any position with considerable power to fully 

 answer its purpose, and the ordinary engine, after an 

 eighth of a revolution of the driving-wheels, has both its 

 cylinders thoroughly effective. In the two-cylinder com- 

 pound the low-pressure cylinder does not get an efficient 



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