12 



SCIENCE. 



[N. S. Vol. XX \ Xo. 523. 



heavy locomotive. So long as the loco- 

 motive was needed to pull a long train of 

 cars, great weight was necessary, and the 

 weight of railway engines and the strength 

 of bridges have been iucreasuig at a rapid 

 x'ate. Wc saw a locomotive at the recent 

 fair at St. Louis Aveighing over 200 tons. 

 It Avas a monster, indeed. Should such 

 locomotives become common, every bridge 

 in the country would have to be rebuilt. 



But when each car, whether for pas- 

 sengers or for freight, has its OAvn motor 

 and drives itself, the heavy locomotive is 

 no longer needed. Moreover, the car itself 

 should be made as light as possible con- 

 sistent with strength. Weight is of no 

 advantage to a self-driven car. The 

 bicycle has taught us a great lesson in the 

 art of construction. A maximum of 

 strength and stiffness with a minimum of 

 . weight. This already prevails in girders 

 and bridge constructions. The same prin- 

 ciples should be applied to all rolling stock 

 and moving machinery. Tubular axles, 

 tubular spokes, tubular fellies, tubular 

 shafts, tubular everything is to be the laAv 

 of future construction. All the great 

 steam-engines and propellers already have 

 holloAV shafts, and I predict an enormous 

 increase in the amount and precision of 

 hollow steel tubing manufactured and used 

 in the next ten years. The mechanical and 

 material advantage of tubular shafting is 

 easily stated. Thus: (1) If a solid 

 cjdindrical shaft be compared Avith a 

 holloAv shaft of the same Aveight per foot 

 of length, but Avhose exterior diameter is n 

 times as great, the strength of the holloAv 

 shaft in torsion is 2n — 1/n times as great 

 as that of the solid shaft. (2) If only 

 equal strength is required, the solid shaft 

 having one nth of the diameter of the tube, 

 Avill weigh 2n — 1/n- times as much. For 

 a numerical example: (a) A thin tubular 

 shaft four inches in diameter is seven and 

 three fourth times as strong as. a solid shaft 



one inch in diameter AA-hich weighs the 

 same per linear foot. 



(&) A solid shaft Aveighs seven and 

 thirty-one thirty-seconds (call it eight) 

 times as much as a tubular shaft of equal 

 strength and four times its diameter. 



The ratio of stiffness of the tube to that 

 of the solid shaft is even greater. 



At the recent St. Louis fair a prize of 

 $2,500 Avas offered for the lightest motor 

 per horse poAver. Motors up to 100 horse 

 poAver were eligible. The prize Avas not 

 aAvarded, for the reason that iuA'entors and 

 constructors of motors were not prepared 

 to submit their apparatus to the rigid tests 

 required for efficiency and durability; but 

 the offer was made Avith distinct intention 

 of stimulating the constriiction of motors 

 which should be suitable for vehicles Avhere 

 lightness combined with great strength is 

 a desideratum, such as in automobiles and 

 air-ships. 



STEEL AND CONCRETE AND CEMENT. 



I scarcely need call your attention to 

 the important part Avhich steel-concrete 

 constructions are destined to play in fu- 

 ture structures. Originally all important 

 bridges. Avails and dams Avere built of 

 stone, and masonry flourished as a fine art. 

 Arches, groined and cloistered, segmental 

 and gothic, elliptic and parabola, combined 

 to make cathedrals and chapels ])eautiful, 

 and bridges stately and strong as Avell as 

 durable. Then came the era of iron and 

 steel, and stone bridges Avere built no more. 

 Steel trusses, posts and girders took the 

 place of stone Avails and granite arches. 

 We are noAV going back to masonry Avails 

 and to masonry bridges, but the masonry 

 is no longer granite ; it is concrete reen- 

 forced by steel. Evidently the opening for 

 engineering theory and engineering enter- 

 prise is most extensive. The ncAv material 

 is not subject to corrosion, so it Avill not be 

 eaten up by rust. It is incombustible, and 



