British Association for the Advancement of Science. 137 



creased, the resistance is increased, but not in so great a ratio as 

 the load. 4, Therefore, the resistance does not, as has been 

 hitherto supposed, bear an invariable ratio to the load, and ought 

 not to be expressed at so much per ton. 5. The amount of the 

 resistance of ordinary loads carried on railways at the ordinary 

 speeds, more especially of passenger trains, is very much greater 

 than engineers have hitherto supposed. 6. A considerable, but 

 not exactly ascertained proportion of this resistance is due to the 

 air. 7. The shape of the front or hind part of the train has no 

 observable effect on the resistance. 8. The spaces between the 

 carriages of the trains have no observable effect on the resistance. 

 9. The train, with the same width of front, suffers increased re- 

 sistance with the increased bulk or volume of the coaches. 10. 

 Mathematical formula, deduced from the supposition that the re- 

 sistance of railway trains consists of two parts, one proportional 

 to the load, but independent of the speed, and the other propor- 

 tional to the square of the speed, have been applied to a limited 

 number of experiments, and have given results in very near ac- 

 cordance, but the experiments must be further multiplied and 

 varied, before safe, exact, and general conclusions can be drawn. 

 11. The amount of resistance being so much less than has been 

 hitherto supposed, and the resistance produced by curves of a 

 mile radius being inappreciable, railways laid down with gradi- 

 ents of from 16 to 20 feet a mile have practically but little dis- 

 advantage compared with a dead level ; and curves may be safely 

 made with radii less than a mile ; but further experiments must 

 be made to determine a safe minor limit for the radii of such 

 curves ; this principle being understood to be limited in its appli- 

 cation to railways intended chiefly for rapid traflic. 



Dr. Ure read a paper on the specific gravity or density of 

 steam at different temperatures. Mr. E. Hodgkinson detailed 

 some experiments made to ascertain the power of different spe- 

 cies of wood to resist a force tending to crush them. The 

 specimens for experiment were turned into right cylinders, 

 about an inch in diameter and two inches long. Great discre- 

 pancies were found when the woods were in different degrees 

 of dryness ; wet timber, though felled a considerable time, 

 bearing in some instances, less than half of what it bore when 

 dry. — Mr. G. Cottam gave an account of the Marquis of Twee- 

 dale's patent brick and tile machine. — Mr. Fairbairn related some 



Vol. XXXVIII, No. 1.— Oct.-Dec. 1839. 18 



