Royal Society. 49 



approach each other, and the latter recede from each other ante- 

 riorly. Intermediate to these are the longer ribs connected with the 

 dorsal arch, having their cartilages united, and articulated with the 

 lower end of the sternum. The scaleni muscles invariably act during 

 the whole time* of inspiration. The external intercostals between 

 the thoracic ribs are also throughout inspiratory ; but those portions 

 which are situated between their cartilages are expiratory ; and 

 those between the diaphragmatic ribs are inspiratory behind, expi- 

 ratory to the side, and in front, and inspiratory between their carti- 

 lages. Between the intermediate ribs, they are for the most part 

 slightly inspiratory between the ribs, and expiratory in front, be- 

 tween the cartilages. The external intercostals of the thoracic ribs 

 are expiratory behind, and inspiratory in front, if the ribs approach 

 these, and are inspiratory between their costal cartilages. Between 

 the diaphragmatic and intermediate sets of ribs, and between their 

 cartilages they are throughout expiratory. The levatores costarum 

 draw the posterior portion of the lower ribs backwards. In the ass 

 and the dog, the upper fasciculi of the serratus magnus are expira- 

 tory, the lower inspiratory, and the intermediate neutral. In man, 

 the greater part of the fasciculi of this muscle is expiratory. In the 

 ass, the lower fibres of the serratus posticus inferior are inspiratory, 

 and the upper fibres expiratory. In the dog and in man, all are 

 throughout expiratory. 



February 26. — " Illustrations of the Viscous Theory of Glaciers." 

 By James David Forbes, Esq., F.R.S. &c. Part III. 



The author inquires, in this part of his paper, into the motion of 

 those comparatively small isolated glacial masses, reposing in the 

 cavities of high mountains or on cols, and called by De Saussure 

 glaciers of the second order. A glacier of this description in the 

 neighbourhood of the Hospice du Simplon, lodged in a niche on the 

 northern face of the Schcenhorn, immediately behind the Hospice, 

 and at an elevation of about 8000 feet above the sea, was selected 

 for observation. The average velocity of its descent was found to 

 be about one inch and a half in twenty-four hours ; those parts in 

 which the slope was 20° moving with a velocity about one-third 

 greater than those in which the slope was 10°. The author next 

 enters into general views on the annual motion of glaciers, and on 

 the influence of seasons ; and gives tabular details of the observa- 

 tions made with reference to these questions at two stations ; the 

 one on the Glacier des Bossons, and the other at the Glacier des 

 Bois, which is the outlet of the Mer de Glace towards the valley of 

 Chamouni. In both these glaciers, the motion in summer exceeds 

 that in winter in a greater proportion as the station is lower, and 

 consequently exposed to more violent alternations of heat and cold. 

 He also found that the variations of velocity due to season are 

 greatest where the variations in the temperature of the air are 

 greatest, as in the lower valleys ; excepting that variations of tem- 

 perature below the freezing-point produce scarcely any appreciable 

 change in the rate of motion of the ice. He concludes with some 

 general illustrations of the plastic or viscous theory of glacier mo- 



Phil. Mag. S. 3. Vol. 29. No. 191. July 1846. E 



