370 



NATURE 



{Sept. 2, 1875 



With a sliding seat, therefore, we seem to have a pro- 

 vision for greater range of movement at the distal end of 

 the lever. In the upper extremity it seems to me we find 

 the same principle at work, and if so it is curious that we 

 should have adopted as a novelty or an invention what 

 nature has provided us with in other points, that we 

 should apply to the lower extremities in rowing the same 

 principle that already exists in connection with the upper, 

 and is brought into action perhaps especially in rowing, 

 and that this should have been done unknowingly. 



The bony framework of the upper limb is connected 

 with that of the trunk at only one point, the inner or 

 sternal end of the collar-bone, and it is round this point 

 that movement occurs. The greatest freedom of motion, 

 however, takes place at the shoulder-joint, and as this 

 joint is, moreover, at the apparent junction of the free 

 limb with the body, the movements here are generally 

 looked into to the exclusion of those at the junction of 

 the collar-bone and breast-bone. But the importance of 

 the latter will at once be recognised when it is considered 

 that the collar-bone and shoulders rotate round the upper 

 part of the breast-bone, and according to their length and 

 mobility will move through a larger or smaller arc. 



The amount of movement between the extremes of for- 

 ward and backward positions of the shoulder (Figs, i 

 and 2) can be readily tested, and I have found that the 

 average of several observations on different individuals, 

 taken at the tip of the shoulder, the chest being abso- 

 lutely fixed, is from six to seven inches ; or, in other 

 words, the tip of the shoulder moves backwards and 

 forwards to that extent between the extremes of forward 

 and backward movement. 



Similarly in the vertical line a large extent of motion 

 occurs, the difference between the extremes being on the 

 average four inches. Now, when it is noticed that the 

 arm moves at the shoulder-joint with an extraordinary 

 amount of facility, and that its chief motions as a 

 m -chanical appendage to the trunk occur in that articula- 

 tion, we are led to look upon the arm, fore-arm, and hand 

 as a compound lever, working with its one end free and 

 the other rotating in the socket of the shoulder-joint. 



In the lower extremity we also find the compound lever 

 working with one end somewhat similarly in a socket. 

 In the case of the upper, however, the socket is a movable 

 one, slipping backwards and forwards freely with the 

 limb and strangely increasing its range of motion ; still 

 capable of being fixed firmly in position by the superficial 

 muscles of the back. But in the lower extremity the 

 socket is fixed, and there is no provision for sliding, since 

 strength rather than range of motion is wanted, and 

 where greater range of motion is needed, as in rowing, 

 there a blind application of the principle found in the 

 upper extremity has been only recently effected. 



I have referred only to the sliding fulcrum at the 

 shoulder as seen on both sides equally, and as is best 

 exemplified in the position of the arms in rowing, when 

 however the whole trunk also moves ; but it must be 

 borne in mind that a still further sliding of the fulcrum is 

 constantly taking place when one hand alone is used, for 

 the chest is also turned towards the object to be reached, 

 by rotating and flexing the spine. The advantage of the 

 vertical motion is seen in such actions as bell-ringing, 

 weight-Ufting, &c. Moreover it must be noticed that 

 when the lever forming the arm is raised from the side to 

 a rightlangle with the body it has reached its Hmit of 

 motion at the shoulder-joint, and that subsequently the 

 upward motion occurs in the collar-bone, since the top of 

 the shoulder checks the further movement of the arm 

 upwards. There is in connection with the lower extremity 

 a somewhat similar mechanical arrangement, which is not 

 however brought into play so fully as in the upper. The 

 sockets of the hip-joints can be brought forward by a 

 rotation of the spine. This is especially noticeable in 

 those who are prevented from using their feet freely, where 

 therefore the elasticity and spring which are so wonder- 



fully provided in the foot are lost, and the length of stride 

 is obtained by the utmost use of mechanical advantages 

 commonly unused in connection with the hip. Plough- 

 men and labourers whose feet are cased in unyielding 

 clogs walk from the hips, or in other words they slide the 

 fulcrum forwards by rotating the spine, whereby they 

 gain a larger stride. 



Fig. 3.— Diagram to show sliding-seat actional the shoulders. In the forward 

 position the arm is thrown forward so that the shoulder is about three to 

 four inches in front of the spinal line s A t. In the backward position the 

 same point is about one to two inches behind the same line s' a' t' , the 

 whole movement occurring at the sterno clavicular articulation. The 

 sliding of the tuberosities of the ischia backwards in this movement is 

 equal to about eight inches (t to t'). The dotted lines show the degree 

 of forward or backward movement of the body which w»uld be necessary 

 to gain the same range of arm-movement, if the tuberosities were fixed 

 and no sliding were used. 



Such then are some of the curiosities of animal me- 

 chanics seen in our wonderful framework, and the subject 

 would repay us in interest as well as in usefulness if 

 studied more by those who are concerned in mechanics 

 generally. W. W. Wagstaffe 



St. Thomas's Hospital 



THE BRITISH ASSOCIATION 



Bristol, Tuesday Night 



OUR meeting has nearly run its course, and may so 

 far be pronounced a great success. BriUiant 

 weather has been added to hospitaUty and to skilful 

 direction, and has produced a generally harmonious 

 result. We may certainly expect that the Association, 

 not less than the Bristol people, will desire a repetition of 

 the visit within somewhat fewer than forty years. 



Partly owing to the comparative weakness of the 

 President's voice, and partly to the deficient acoustic 

 properties of Colston's Hall, the President's address was 

 not quite so successful as it might otherwise have been. 

 Even Prof. Tyndall had to strain his voice considerably 

 in order to be well heard. Perhaps the most forcible 

 ideas left on the mind by Sir John Hawkshaw are his 

 patience and caution, his dislike for taking leaps in the 

 dark, and his eager desire to take steps in advance when 

 the way can be seen with tolerable clearness. His 

 modesty in not referring to any of his own great achieve- 

 ments, when pertinent references might have been made, 

 was very noticeable. Prof. Tyndall, in his admirable 

 opening address, spoke as follows : — 



" It is my privilege to introduce to you as your president 

 for the coming year Sir John Hawkshaw, a name cele- 

 brated throughout the world for the practical application 

 to works of the greatest magnitude of some of these 

 sciences which it is the function of this Association to 

 foster and advance. In him, I doubt not, you will have 

 a wise and prudent head, a leader not likely to be caught 



