38o 



NA TURE 



[February 17, 1898 



I.H.P. was 5'io, the gas per I.H.P. per hour 2035 cubic ^^^'^^ 

 the heat expended per liH.P. per hour was 12,186 thermal 

 units, or 10 "95 thermal units per explosion. The thermal efficiency 

 was 21 per cent. Taking one of the low-speed experiments, 

 with the ratio of air togas of iO'4, the compression per square 

 inch absolute was 86 lbs., the ratio of clearance to cylinder 

 volume was 0'37, the revolutions per minute were II7'6, 

 and the ratio of actual explosions to the maximum possible 

 was 75 per cent. With these conditions the I.H.P. was i '84, 

 the gas used per I.H.P. per hour 28*2 cubic feet, the heat ex- 

 pended was 17,041 thermal units per I.H.P. per hour ; that gave 

 a thermal efficiency of 15 per cent., a result which, as the author 

 remarks, was distinctly uneconomical. In the following test the 

 compression was 102 lbs. absolute, the ratio of clearance to 

 cylinder volume being o'25, the revolutions and the I.H.P. were 

 practically the same, but 31 cubic feet of gas were used per 

 I.H.P. per hour ; the thermal efficiency, therefore, being 13 '6 per 

 cent, although the compression was so much higher than in the 

 previous test mentioned, almost approaching that of the full- 

 speed test first referred to. 



In connection with this matter, the fact commented upon 

 during the discussion may be referred to. The older gas engines 

 were designed for lower pressures ; and it is found with them that 

 increasing the compression does not add to economy. The ratio of 

 clearance has an important bearing on the case, the port sur- 

 face acting as a condenser, and an increase in the compression 

 induces a degree of cooling which is not economical. There is 

 also the loss by leakage through the indicator, the proportion 

 of which will be considerable in the case of a small engine. 

 The Wayne indicator used during the experiments has a rotating 

 piston not touching the sides of the cylinder, and therefore 

 admitting of constant leakage. In the steam engine the loss 

 from leakage through the indicator is comparatively unimpor- 

 tant, being governed by the pressure present in the cylinder 

 at any given time. With the gas engine, however, this is 

 different, as the working mixture escapes through the cylinder 

 before ignition. One of the speakers humorously likened the 

 effect of an indicator on a small gas engine to a big whistle 

 on a steam launch b alt r. He said that in the early days of 

 steam launches a friend of his had a small paddle yacht with 

 a very big whistle, which was fitted in order that he might let 

 his friends know when he was coming. He found, however, 

 that when he paddled he could not whistle, and when he 

 whistled he could not paddle. 



A brake was used in the experiments, and perhaps it would have 

 been better if Brake H.P. had been given in the tables. It was 

 found that the measurement of gas by means of an ordinary 

 meter, although giving a correct aggregate result, possessed the 

 disadvantage of not controlling the fluctuations of pressure in 

 the mains ; a calibrated gas-holder was therefore used. The 

 amount of air used per stroke was measured by a meter into 

 which air was forced by a Sturtevant blower, the pressure being 

 kept constant by means of a gas governor ; precautions were 

 taken to prevent back ignition ; a rubber gas bag was used to 

 obviate the fluctuation in pressure in the meter during the 

 suction stroke. No difficulty was found in working this ap- 

 paratus. Records were taken of pressure and temperature of 

 the air ; measurement of the heat rejected was effected by run- 

 ning the cooling water from the calibrated tank through the 

 water jacket and thence to the discharge, the capacity of the 

 tank being sufficient to hold water for a single test. The 

 temperatures of the inlet and outlet water were taken. The glass 

 stems of the thermometers were attached to brass plugs by means 

 of soldering with Thomas's fusible metal, which enables glass 

 and brass to be fixed together with a pressure-tight joint. 

 To obtain samples of the exhaust gases, a single bubble 

 of gas was taken from just below the exhaust-valve after each 

 explosion stroke by means of suitable apparatus, which was 

 illustrated by a wall diagram shown during the reading of the 

 paper. The Wayne indicator used to find the I.H.P. 

 was considered superior to the Richards, Crosby, Darke or 

 Tabor indicators. It was made by Messrs. Elliot Brothers. 

 This indicator appears to be similar in principle to one intro- 

 duced by Mr. Michael Longridge some years ago. For reducing 

 pencil friction to a minimum, cards of smoked mica were intro- 

 duced in place of the usual paper. An iron tube was used for 

 ignition, electrical methods having been tried, but were not 

 found satisfactory. 



The author, in giving a summary of the experiments, concluded 

 that it was probable that the influence of increased compression 



NO 1477. VOL. 57] 



on economy was due to the fact that weaker charges can be burnt 

 completely during the stroke when the compression is high. It 

 should be stated that in the test of which we have given par- 

 ticulars, in which the thermal efficiency was 21 per cent., the 

 author considered that more economical results than this 

 could be obtained, as the ratio of air to gas was 8 '6, which 

 was certainly higher than necessary. It may be added that the 

 best mixture for a modern gas engine is considered to be one 

 of gas to ten of air by volume. The report continued that 

 the test seemed to indicate that economy depends on the 

 choice of the correct ratio of air to gas, and that this ratio 

 increases with compression. The number of experiments was 

 not yet sufficient to determine what any ratio was for any 

 given compression, but it is stated that further tests are to be 

 made for arriving at this important point. 



The summer meeting of the Institution will be held this year 

 in Derby. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — Mr. Charles Godfrey, of Trinity College, has 

 been elected to the Isaac Newton Studentship in Physical 

 Astronomy. 



The General Board of Studies propose that the Professorship 

 of Surgery, held by the late Sir George Humphry, be suspended 

 until the Senate shall otherwise determine. Meanwhile the 

 duties of the office are to be discharged by a Reader in Surgery, 

 at a stipend of 240/. a year. 



The General Board also propose to recognise the continued 

 liberality of the Royal Geographical Society in providing for the 

 endowment of geographical teaching, and the importance of 

 encouraging the study of the subject in the University by raising 

 the present Lecture.ship, held by Mr. Yule Oldham, to a 

 Readership in Geography, with a total stipend of 200/. a year. 



Dr. Karl Hurthi.e, assistant professor of physiology at 

 Breslau, has been appointed professor of physiology and 

 director of the Physiological Institute, in succession to the late 

 Prof. Heidenhain. 



The Council of King's College, London, have received from 

 the Trustees of the British Museum a valuable series of fossils, 

 in aid of the teaching collection for the Geological Laboratory 

 in the Science and Engineering Faculty. 



An anonymous donor has offered 10,000/. for the completion 

 of the extension scheme of Aberdeen University, on the condi- 

 tion that 20,000/. is obtained from the Government for the same 

 object. The Chancellor of the Exchequer has agreed to receive 

 a deputation on behalf of the movement for the extension of the 

 University. 



Science states that at the semi-annual meeting of the Board 

 of Trustees of Beloit College it was announced that the College 

 had received a gift of 25,000 dollars for the endowment of the 

 chair of Chemistry, now occupied by Prof. E. G. Smith. The 

 donor wishes to remain anonymous. It was also reported that 

 the sum of 70,000 dollars had been raised towards the 100,000 

 dollars necessary to secure Dr. Pearson's gift of 50,000 dollars. 



The rapid progress of medical education and the enlargement 

 of the requirements of the Examining Boards have rendered it 

 imperative to provide more space for the teaching of several im- 

 portant subjects in the London Hospital Medical College. 

 Consequently a large portion of the College is about to be re- 

 built and enlarged, and all the necessary class-rooms and labora- 

 tories provided. It is intended that the work will be completed 

 by the commencement of next winter session. 



The magnitude of the operations of the Department of 

 Science and Art may be judged from the figures given in the 

 Calendar of the Department for 1898. The total number of 

 individual students in science classes held under the auspices of 

 the Department was 157,984. The subjects which attracted 

 more than ten thousand students in the year covered by the 

 Calendar are : Mathematics (Stages i, 2, 3), 40,244 ; In- 

 organic Chemistry (Theoretical), 26,433 ; Practical Plane and 

 Solid Geometry, 24,069 ; Physiography, 22,409 ; Machine 

 Construction and Drawing, 19,952 ; Building Construction, 

 15,195; Magnetism and Electricity, 12,591 ; Hygiene, 10,143. 

 At the other end of the scale we find that mineralogy only 

 attracted 152 students, and zoology 189. Nine of the depart- 



