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 formule, 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 traffic. 
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- 
“ies 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 i in some instances, less than half of what it bore wheit 
dry.—Mr. G. Cottam gave an account of the Marquis of Twee- 
_ dale’s patent brick and tile machine.—Mr. Fairbairn related some 
=>Vul, xxxvur, No, 1.—Oct.-Dec. 1839. 18 
