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a single line, especially with numerous stations. When a great velo- 

 city is obtained, the tractive force of the locomotive is much re- 

 duced, and therefore a much greater velocity can be attained on an 

 atmospheric railway. 



The inquiries of the author into the amount of resistance exerted 

 by the air on railway trains lead him to the conclusion that in the 

 atmospheric railway the loss of tractive power of the piston from 

 friction, &c. is very inconsiderable ; and that the resistance of the 

 air is less than had been hitherto estimated, not exceeding, on an 

 average, ten pounds per ton on the average weight of trains. 



A tabular statement is then given of the results of the experi- 

 ments made by the British Association, for the purpose of com- 

 paring them with those obtained by the author from his own ob- 

 servations, and more particularly from his experiments on the Croy- 

 don Atmospheric Railway. The general conclusion which he draws 

 from this investigation is that the resistance of the air in a qui- 

 escent state is less than had been previously estimated, and that the 

 ordinary atmospheric resistance in railway progression arises from 

 the air being generally itself in motion, and as the direction of the 

 current is almost always oblique, from its producing increased fric- 

 tion in the carriages themselves. This kind of resistance will not 

 increase as the square of the velocity; and as it is the principal one, 

 it follows that the resistance to railway trains increases in a ratio 

 not much higher than the velocity, and that the practical limit to 

 the speed of railway travelling is a question, not of force, but of 

 safety. 



March 26, 1846. 

 The MARQUIS OF NORTHAMPTON, President, in the Chair, 

 George Newport, Esq. v/as elected a Fellow of the Society. 



" On the Muscularity of the Iris." By Professor Maunoir, of 

 Geneva. Communicated by P. M. Roget, M.D., Sec. R.S. 



The author has satisfied himself, from the result of his own dis- 

 sections, as well as from the concurrent testimony of a great number 

 of anatomists, that the iris is provided with two sets of muscular 

 fibres, the one orbicular, immediately surrounding the pupillary 

 margin and acting as a sphincter ; the other, extending in a radiated 

 direction from the exterior circumference of the former to their in- 

 sertions into the ciliary ligament, their action being to enlarge the 

 pupil. One-fourth of the disc of the iris is occupied by the orbi- 

 cular, and the remaining three-fourths by the radiated muscle. The 

 author has examined the structure of the iris in a great number of 

 animals, and states the results obtained by M. Lebert, v/hom he 

 applied to on this occasion, from numerous dissections of the eyes 

 of animals belonging to each class of vertebrata. He also refers to 

 a work which he published in the year 1812, entitled " Memoire sur 



