August 5, 1909J 



NA TURE 



m 



iiected to the engine cylinder, and the indicator diagrams 

 were talien simultaneously. The indicator barrel of the 

 Crosby indicator was rotated by a phosphor-bronze 

 stranded wire wound round the barrel and led to a bell- 

 crank lever. The bell-crank lever was driven by a steel wire 

 attached to the usual lever driven by the engine piston. 

 .\ very heavy spring, in which a compression of 400 lb. 

 produced a contraction of 2 inches, controlled the bell- 

 crank lever. The optic indicator was also driven by means 

 of a phosphor-bronze stranded wire. 



The mean diagrams were prepared from no fewer than 

 twelve individual diagrams, each being divided by the 

 method of ordinates, and the heights read by an accurate 

 steel rule. With care it was possible to read the Crosby 

 diagrams to an accuracy of half of i per cent. The optic 

 indicator diagrams could readily be measured to the same 

 order of accuracy. The diagrams were plotted on squared 

 paper, and superposed one on the other, so as to exhibit 

 whatever differences there were between the indicators. 



Speaking generally, the compression curves are coincident. 

 The maximum, pressures practically agree in two of the 

 tests ; in a third, the Crosby indicator gave the higher 

 initial pressure, and in the fourth the Hopkinson gave the 

 higher. Down the expansion line the two indicators agree 

 for the third of the stroke. After that the Hopkinson indi- 

 cator gave a persistently higher expansion line, the difference 

 between the two lines being higher than the probable ex- 

 perimental error of the measurements. The effect of this 

 difference is to make the Hopkinson indicator give about 

 3 per cent, higher mean pressure than the Crosby. 



In the Hopkinson indicator the spring vi'as in the form 

 of a flat bar rigidly fixed at the ends and loaded in the 

 centre ; the central deflection of this beam is a direct 

 measure of the pressure on the piston. During calibration 

 with dead weights, from which the scale of the spring is 

 obtained, the ends of the bar may be assumed to be 

 absolutely fixed, but when the indicator is in use it is 

 possible that there is a slight slip in the bar through the 

 screws which restrain it. The effect of this would be to 

 prevent the pressure falling so rapidly in this indicator 

 as in the Crosby indicator. The author believes that this 

 explanation is more likely to be correct than that the 

 effect is due to inertia or friction, and is inclined to prefer 

 the results obtained from the Crosby indicator. 



While the results of this comparison do not offer an 

 absolute proof of the accuracy of either indicator, there 

 is still strong evidence that both give results very close 

 to the truth. The indicators are of entirely different types, 

 one multiplying the indicator piston movement by six, 

 the other by about 120, a very similar multiplication 

 being the case with the rotation of the drum and the 

 mirror. In the optic mirror inertia is certainly negligible. 

 That the two give results to within 3 per cent, on the 

 mean pressure, and very nearly the same figures for the 

 initial pressure, is good presumptive evidence that, when 

 either indicator is used with the precautions regarding 

 driving described, the results so obtained are at least as 

 accurate as any other measurement which can be made 

 in engine testing. Unless these precautions are taken, the 

 results can only be regarded as affording a clue to the 

 valve setting, and give no trustworthy figures as to the 

 power developed in the engine cylinder. 



The council of the institution has issued the conditions 

 under which the second award of the water arbitration 

 prize will be made in iqio. The prize will have a value 

 of about 30!., and will be awarded to the author of the 

 best original paper dealing with any branch of the 

 mechanics of the supply or distribution of water. The 

 latest date for sending in papers will be September i, 



IQIO. 



I 



MR. HALDANE ON THE PROMISE OF 

 A VIA TION. 



N Committee on the vote of 36,464?., including a sup- 

 plementary sum of 6500/., to complete the sum 

 necessary to defray the charge for sundry grants in aid, 

 scientific investigation, and other grants, there was an 

 interesting discussion in the House of Commons on 

 .August 2 on the subject of aviation for naval and military 

 purposes. Mr. Haldane made a statement giving the 

 views and intentions of the Government. 

 NO. 2075, VOL. 81] 



Mr. Haldane said he had made up his mind that there 

 could be no real progress unless we proceed scientifically 

 and in order — that is to say, unless we are perfectly clear 

 about what we want, as to the structure of the machines 

 which will be used for the purposes in view, and the pro- 

 duction of them in a way which should be at least 

 effective. The first thing done was to ask the Committee 

 of Imperial Defence to investigate this question and to 

 discuss it with the technical subcommittee. The report 

 was to the effect that the class of machines must be 

 divided into three heads : — rigid dirigibles, non-rigid 

 dirigibles, and aeroplanes. For naval purposes the rigid 

 dirigible is probably the only instrument of the kind which 

 is of real value, at any rate in the present state of know- 

 ledge. For the army the rigid dirigible has certain dis- 

 advantages. It is more difficult to work, to bring back, 

 and to bring to rest. It is more diflicult for the army 

 than for the navy. The non-rigid dirigible is the best for 

 army purposes. The aeroplane may become available for 

 army purposes, but at present it has certain defects. It 

 will have to rise much higher before it can be a safe 

 instrument for reconnoitring. But M. Bleriot's splendid 

 feat in crossing the Channel and the successes achieved in 

 the United States point to a time when the aeroplane 

 may be an instrument capable of achieving great results. 



To the navy has been assigned the duty of investigating, 

 with the view of constructing, the rigid dirigible, the ship 

 of the Count Zeppelin type. To the army has been 

 assigned the duty of experimenting with the non-rigid 

 dirigible, the machine of varying type, and also with 

 aeroplanes. 



To make their study of aviation scientific, Mr. Haldane 

 said the Prime Minister constituted the advisory com- 

 mittee, under Lord Rayleigh's presidency, on which there 

 is some of the best scientific brains in the world. Con- 

 tinuous work has been going on at the National Physical 

 Laboratory. Meetings have been held there and at 

 Aldershot and the War Office. The committee is to 

 advise, its purpose is to scrutinise inventions submitted 

 in the course of the work of the departments concerned, 

 and to conduct systematic experiments. In a few days 

 the first report of this committee will be made public. 

 The committee, said Mr. Haldane, has such men as Lord 

 Rayleigh and Dr. Glazebrook on it, and such men on 

 the practical side as Mr. Lanchester and Mr. Mallock, 

 and others like Prof. Petavel and Dr. Shaw, and also 

 such high authorities on the army and navy side as 

 Major-General Haddcn and Rear-Admiral Bacon, and is 

 well furnished froni the various points of view. This 

 committee has been at work, and the first thing it has 

 done is to determine the general question which should 

 be studied. There have been various memoranda by the 

 experts on stability, screw propellers, wind structures, 

 petrol motors, and a very difficult thing which has arisen 

 in connection with balloons, the accumulation of electro- 

 static charges. Everyone knows what a peril electricity is 

 in the air. Then the committee has mapped out the 

 general field of its work. There are certain general qties- 

 tions in aerodynamics, questions specially relating to aero- 

 planes, such as the mathematical investigations of 

 stability, the effect of rudder action, gusts of wind, and 

 half a dozen other things which I need not emimerate. 

 There are propeller experiments ; there are questions re- 

 lating to these motors which have to be of special con- 

 struction for air work, general questions relating to air- 

 ships, and still more general questions relating to 

 meteorology. 



The committee has entered into communication with the 

 Aeronautical Society, the Aerial Club, and the A(>ro 

 League. The design is to afford assistance to private 

 inventors wherever this can properly be done, because 

 progress in this matter will be. not merely a Government, 

 but a national matter. The Admiralty is concentrating, 

 under Admiral Bacon, Director of Naval Ordnance, on 

 the building of a rigid dirigible of the very largest type, 

 at least the size of the Zeppelin. That is being builtat 

 Barrow-in-Furness by Messrs. Vickers. The combination 

 of experts and practical men may give us a practical 

 result some time next spring. The War Office is re- 

 organising its factory at Aldershot. The instruction, which 

 is "at present given to balloonists under the superintend- 

 ence of Colonel Capper, is being separated from construe- 



