NA TURE 



\_July 3, i< 



able here. More space is occupied by the London School 

 Board, whose lending libraries for schools and reference 

 libraries for pupil teachers are well selected. The geo- 

 graphical teaching cannot, of course, be compared with 

 that on the Continent, though some of the district maps are 

 good. Fair provision is made for teaching science to pupil 

 teachers, but there is a lamentable deficiency in the ap- 

 paratus for this and for the whole system of object-lessons, 

 when the needs of the scholars themselves are considered. 

 The School Boards of Edinburgh and Glasgow show 

 some excellent models, photographs, and plans of school 

 buildings of the newest type, and some remarkable speci- 

 mens of drawing. The Wesleyan Education Committee 

 show some excellent results of the scientific and handicraft 

 training of boys, and some very simple yet remarkably 

 effective appliances for elementary geographical instruc- 

 tion. 



Although these collective displays by public bodies are 

 the most interesting feature of this portion of the Exhibi- 

 tion, there is much that will repay examination in the 

 various objects shown by many single exhibitors of the 

 great variety of school desks and furniture ; some of the 

 desks of G. M. Hammer, G. E. Hawes, and H. Simon 

 and Co., deserve more than a passing notice, as do also 

 the revolving partitions of Hodkinson and Clarke. 

 Among maps and charts the collection of Mr. E. Stan- 

 ford stands out prominently, and is specially noticeable 

 for the five series of physical and orographical maps, 

 some of which in frames are on continuous sheets and 

 rollers. Mr. Bacon's maps are singularly clear and good 

 for school use, and his picture-lessons in geography are a 

 step in the right direction. The apparatus for teaching 

 music, exhibited by J. Curwen and Sons, is perhaps not 

 approached by any similar exhibit. The science charts 

 and diagrams produced by M. Emile Deyrolle are of an 

 extremely high degree of excellence, and deserve to be 

 made widely known. The educational publications of 

 such firms is Messrs. Cassell and Co., Messrs. Gill and 

 Sons, the Messrs. Johnston, Messrs. Griffith and Farr.in, 

 Messrs. Bemrose and Sons, and Messrs. William Collins, 

 Sons, and Co., who are all well represented, are too well 

 known to need more than a reference. 



In a second article we hope to deal in a similar way 

 with the exhibits of apparatus and results of scientific 

 and technical teaching carried to a higher degree than in 

 mere primary schools, and also, briefly and by way of in- 

 troduction, with that range of subjects which may be 

 shortly described as comprising the technical education 

 of children and girls. It may perhaps be permitted to 

 the writer to say, as the result of a very close examina- 

 tion (extending over more than a week continuously) of 

 the exhibits "relating to primary education in various 

 countries, that one important lesson to be learnt from the 

 comparison of Continental methods with our own is the 

 great advantage afforded by the objective system of teach- 

 ing, and by the adoption of that systematic order and 

 method in all subjects of instruction, literary or other- 

 wise, to which the name scientific, in the highest and best 

 sense of the term, is applicable. 



\\"m. Lant Carpi. n i i r 



WORK-MEASURING MACHINES* 



UNDER this title a little brochure has recently ap- 

 peared from the pen of the Rev. F. J. Smith, B.A., 

 of Taunton, in which work-measuring dynamometers, or 

 ergometers, as the author terms them, of various forms 

 are described. Amongst these machines there are many 

 devised by the author himself, and some of these are of 

 considerable interest and much originality. The trans- 

 mission ergometers of the type orig nally invented by 

 General Morin deserve notice in particular. The follow- 



1 " Work-Me.isu: ng Machines." I'y Frederi k J. Smith, B.A, 32 pp. 

 l2mo. (London : K. and V . N. Spun 1884.) 



ing is the general principle involved in transmission ergo" 

 meters : — 



Let it be supposed that a belt passes over from the 

 driving wheel of a prime-mover such as a steam-engine to 

 the pulley of a dynamo which is being driven. One half 

 of the belt is subjected to a strong pull, the other is rela- 

 tively slack. Then if we could introduce spring balances 

 into the two parts of the belt, and if we could read the 

 difference of the tensions T and 1", and if we multiplied 

 this T - t', expressed in pounds, by the velocity of the 

 belt in feet per second, we should then have the " foot- 

 pounds per second" spent in driving the dynamo. From 

 this we can calculate the horse-power by dividing it by 

 550, since 550 foot-pounds per second is one horse-power. 

 This we may write algebraically : — 



(T - T') 

 H.P. = 5 v : 



55° 



where v denotes the velocity of the belt in feet per second. 

 Now since such an arrangement as this cannot be 

 easily carried out, the usual method is to place between 

 the engine and the dynamo some instrument capable of 

 showing the tension of the belt in pounds, and the velocity 

 of the belt, and in certain cases these instruments can 

 even give a continuous record of the work done. The 

 ergometer devised by Mr. Smith is an admirable in- 

 stance of such a combination, and it undoubtedly pos- 

 sesses points of superiority over all transmission dynamo- 

 meters hitherto inventid. A view of the machine (see 

 figure) shows how the ergometer is arranged. The central 

 shaft, of Whitworth steel, which is tubular at each end 

 and link-shaped between, carries two pulleys. One is 

 keyed to the shaft and carries two bevel-wheels, these 

 engage with another bevel-wheel which forms part of the 

 second pulley, which is loose on the shaft. 



To each of the two bevel-wheels, as shown in the 

 diagram, there is fitted a cylindrical drum, on these either 

 gut or steel tape is coiled over three-fourths of their faces, 

 and the gut or tape is attached to a cross-head. The 

 latter is in turn attached to a cylindrical steel spring 

 placed within the link, and from the cross-head a rod of 

 steel, passing through one end of the link, actuates the 

 pointer of a dial, whereby the pull on the spring attached 

 to the end of the link is shown. This instrument re- 

 sembles therefore the earlier dynamometer of Morin in 

 having two pulleys ; the angular advance of one of them 

 being regulated by a spring. But in Morin's form the 

 spring was simply an extended piece of steel. In the more 

 recent modification by Profs. Ayrton and Perry, coiled 

 >teel springs are also used ; but in that instrument the 

 springs are liable to fly out by centrifugal force, and the 

 arrangement for observing the angular advance is an 

 optical one, requiring an observation of a silvered bead 

 by a reading-telescope. In Mr. Smith's ergometer there 

 is no such tendency of the spring to fly, and the tension 

 is read direct on a dial. The speed indicator is shown 

 just below. If a continuous record of work is required, 

 the steel rod is either attached to a recording drum or to 

 an integrating apparatus. 



The instrument having been placed between a prime 

 mover and a machine to be tested, the belt from the 

 prime-mover drives the loose pulley, and another belt from 

 the fixed pulley drives t'le machine to be tested. The 

 tension on the driving side of the belt causes the spring 

 to be extended by means of the bevel-wheels, and differ- 

 ence of the tensions is indicated by the pointer of the 

 dial. The instrument is calibrated by hanging known 

 weights from strong thin cords or catgut strings passing 

 round the pulleys, and marking the dial in accordance 

 with the weights. 



The springs used by Mr. Smith are made by Messrs. 

 Salter and Co., thev are of four sizes, capable of being 

 extended 2 inches by 50, 100, 150, and 200 lbs. respec- 

 tively. Thev have been put to severe tests, but have come 



