594 



NATURE 



[August 7, 1913 



the north-east of Aberdeen. The remaining vessels 

 are light vessels, two acting- for Holland, the other 

 four, by courtesy of the Brethren of the Trinity, for 

 the English department. 



The observations will consist of current measure- 

 ments made near both surface and bottom every hour 

 night and day, throughout the fortnight, and in fine 

 weather at other intermediate depths. Special atten- 

 tion will be paid to the submarine waves which are, 

 it is expected, to be met with at the depth at which 

 the heavier bottom water and the lighter surface water 

 are in contact; but information will be obtained as to 

 all lay-ers. Specially devised current meters are used 

 in this work, some depending for their operation on 

 small propellers, resembling those of an anemometer 

 and worked by the current, others upon the deflection 

 of a wire from which a metal cylinder depends, caused 

 by the force exerted by the current. The temperature 

 and salinity of the various layers of the sea will also 

 be ascertained in the course of the work, special 

 water-bottles being employed to secure samples 

 of the sea from any desired depth. Samples of the 

 minute floating organisms which, directly or in- 

 directly, constitute the food of all our food "fishes will 

 also be taken at various depths and at the extremes 

 • if 1 he tide. 



Some idea of the scale of the operations may be 

 gathered by the fact that it is expected that some 

 Sooo independent current measurements will be made 

 from the English vessels alone. 



The hydrographic operations are planned by a special 

 committee of the International Council for the Ex- 

 ploration of the Sea. They are undertaken because a 

 knowledge of the constitution and movements of the 

 sea-water is essential to the understanding of the 

 movements and even of the abundance of the fishes 

 upon which our fishing industry depends. As a 

 classical instance, the herring of the Kattegat and 

 Skagerak may be cited. Its abundance or scarcitv 

 has been found to be connected directlv with the 

 amount of water which enters the Baltic from the 

 North Sea ; and, indeed, not only the herring fishery 

 but other fisheries of southern Sweden have been 

 shown to change with the ebb and flow of this laver 

 of cold salt water. It is clear, in fact, that a state 

 of knowledge of marine currents which would permit 

 of prognostication as to their movements and volume 

 at a later per ; od would in the case of many fisheries 

 permit the fishermen to reap the utmost harvest which 

 the year would afford or to anticipate a time of 

 scarcitv and take such precautions as were possible 

 to mitigate its effects. 



A NEW METHOD OF COOLING GAS- 

 ENGINES. 

 T'HE summer meeting of the Institution of 



A Mechanical Engineers was held in Cambridge 

 last week. Among the many papers read and dis- 

 cussed, that by Prof. Bertram Hopkinson, of Cam- 

 bridge University, takes a prominent place ; the sub- 

 ject of the paper was a new method of cooling gas- 

 engines. The most important peculiarity of the^gas- 

 engine, that which determines the characteristic 

 features of its design and operation, is the heat-flow 

 from the hot gases into the cylinder walls. About 

 30 per cent, of the heating value of the fuel passes 

 into the metal of the engine in this way. The method 

 hitherto employed in removing this heat has been by 

 the circulation of water in jackets, except in the 

 case of small air-cooled engines. In large engines, 

 the piston and exhaust valve have also been kept cool 

 by circulation of water. The appliances necessary for 

 the carrying out of this method have been responsible 



NO. 2284, VOL. 91] 



largely for the great weight and cost of large gas- 

 engines. 



Water circulation has secondary effects which tend 

 to make a large engine untrustworthy in working. 

 The cylinder walls in places may be 3 in. thick or 

 more. To cause the heat to flow from the inner to the 

 outer surface of the metal requires a temperature 

 difference of the order of 50 C. per inch, and this may- 

 become serious with thick walls. It is also difficult 

 in large engines to secure adequate circulation about 

 all parts of the cylinder walls and piston, and some 

 parts may be much hotter than others. Severe stresses 

 may be set up in consequence of the unequal expan- 

 sion, and the overheating of certain parts of the inner 

 surface is apt to cause pre-ignition of the charge. In 

 consequence of the dangers of overheating it has been 

 found impossible to work gas-engines, especially of 

 large size, continuously at the maximum power which 

 1 hi y ( an develop. 



In Prof. Hopkinson 's method of cooling, water is 

 injected internally in thin jets directed against the 

 walls of the combustion chamber and the end of the 

 piston. There is thus no heat flow through the metal 

 and no difference of temperature between the inner 

 and outer surfaces. The water is so distributed that 

 each part receives it in proportion to the rate at which 

 it receives heat from the hot gases. Practically 

 uniform temperature all over is thus maintained, and 

 the stresses due to unequal heating are eliminated. 

 A simple single-walled casting can" be used for the 

 cylinder, resulting in a great saving in weight and 

 cost and in improved trustworthiness on account of 

 the elimination of casting stresses. Piston-cooling 

 arrangements— a frequent cause of trouble — can be 

 dispensed with. Finally, pre-ignitions are entirely 

 [n-e\ ented. 



To obtain success in this method of cooling, the 

 water must be projected in comparatively coarse drops 

 or jets directly against the surfaces to be cooled, so 

 that it reaches these surfaces in the liquid form with- 

 out much loss by evaporation on the way. Water 

 which reaches the walls in the liquid form, and is 

 there evaporated, absorbs, out of the heat given to 

 the walls by the gas, the whole of its own heat of 

 evaporation ; there is no loss of thermodynamic 

 efficiency because the heat used is waste heat,' which 

 in a jacketed engine would go to warm the cooling 

 water. Any steam formed in this way is pure gain"; 

 and, if anything, there is an increase in the work 

 done. 



Further, if the cylinder walls are allowed to become 

 and remain wet, they are destroyed rapidly by cor- 

 rosion. This is due to the presence of sulphur dioxide 

 in the gas, which forms sulphurous acid when dis- 

 solved in water. This difficulty has been overcome 

 by regulating the amount of water injected in such a 

 way that the temperature of the whole of the engine 

 is kept well above ioo° C. Under these conditions 

 every drop of injected water is boiled when it reaches 

 the walls, and no liquid can accumulate. It is found 

 to be sufficient to inject water on to the surface of 

 the combustion-chamber and the head of the piston 

 only; the cooling of the barrel is effected by conduc- 

 tion into the piston. Thus no water falls on the slid- 

 ing surfaces, where it would cause damage by the 

 dissolved salts producing grinding. 



Trials have been made on a Crossley engine fitted 

 with a new cylinder embodying the principles explained 

 above. The cylinder is \\\ in. diameter by 21 in. 

 stroke, and is rated at jo brake horse-power at 180 

 revolutions per minute. The success of this engine, 

 as compared with the original water-jacketed cylinder, 

 has been remarkable. After considerable preliminary 

 trials, the engine was put to drive a dynamo in a 



