Prof. Forbes on the Ascent of Moim tains. 261 



female; here also a continued junction of both jj^enders with- 

 out being grown together, and in Syngamus trachealis a con- 

 tinual combination, by being really grown together. 



Explanation of the Figures {Plate L),^ 



Fig. 5. Syngamus trachealis, natural size. 



Fig. 6. The same (another specimen, with much longer male 

 branch) greatly magnified, a. Male branch, b. Fe- 

 male branch, c. Incision into which the generati ve 

 organs descend. 



LI I. On the Muscular Effort required to ascend Planes of 



different Inclinations. By Professor FoRBES.f 

 TT has been long pretty generally knoWn that the same ex- 

 ■^ pense of muscular energy will carry a person through 

 nearly the same vertical height in a given time, at all angles 

 of elevation not very small. At least we find writers on the 

 subject of strength, measuring effort by the number of pounds 

 raised multiplied into the height attained. I am persuaded 

 that this is much more rigorously true than is usually sup- 

 posed, and that a person in uniform health and of a* good 

 habit of body will ascend through almost precisely the same 

 number of vertical feet in an hour (unloaded) whether the 

 ascent be rapid and short, or tortuous and little inclined, ex- 

 cluding, of course, extreme cases. 



All paths by which mountains are usually ascended on 

 foot, lie within these practical limits; the mean angle of 

 ascent on footpaths varying in different cases from 10° to^S"^, 

 seldom being below the former, and almost never exceeding 

 the latter. In fact, the angle of ascent is determined, not so 

 much by the configuration of the ground as by the instinctive 

 (or rather experimental) modification which the walker gives 

 to it by such zigzag courses as increase the length and dimi- 

 nish the steepness of the path. This makes the difference of 

 ascent less than might at first be supposed. Thus the time 

 required to ascend a mountain whose height is known, may 

 be pretty accurately predicted by any individual who has de- 

 termined the measure of his muscular energy ; and conversely, 

 heights maybe deduced from the times of ascent with surpris- 

 ing accuracy, a result of great use when more exact methods 

 cannot be employed. 



From the observation of Borda upon the men who accom- 

 panied him in ascending the Peak of Teneriffe, the ascensional 

 effort was 1225 English feet per hour, continued for eight 



* The Plate was given in the Number for March. 

 t Communicated by the Author. 



