252 DR. A. RANSOME ON GRAPHICAL REPRESENTATION 



which it would produce if its movements were governed 

 simply by the mechanical conditions of the cos to -vertebral 

 joints, and by the length and obliquity of the chord-line 

 drawn from its anterior extremity to its head. 



In consequence of these indications, it seemed desirable 

 that exact graphical tracings of the course described by 

 the ends of the ribs should be obtained, in order that their 

 peculiarities in different cases might be studied. 



The chief difficulty in the way of obtaining these tracings 

 was found in the fact that the course of the movement lay 

 in three planes, instead of in two only. 



Observations with the three-plane stethometer, how- 

 ever, had shown that the degree of outward or lateral 

 motion possessed by the ends of the ribs was very small, 

 and that the measurements of this movement were of much 

 less importance than those of the other two, which carried 

 with them interesting practical indications. 



It seemed better, therefore, to sacrifice the registration 

 of this, the lateral motion, for the sake of bringing the up- 

 ward and forward movements into the same plane. It 

 was easy to do this by resting the whole apparatus, both 

 the pencil and the ground upon which the course was de- 

 scribed, upon a swivel joint, which permitted free rotation 

 with any lateral movement of the chest- wall ; and in ex- 

 periments upon the ends of the ribs this motion is so small, 

 that it produces no perceptible effect upon the movements 

 in the upward and forward direction, and any error that it 

 introduces may safely be neglected. 



The stethograph, then, which I have devised consists of 

 a lever (l) , 6 inches long, having a pad (b) at one end, con- 

 nected with it by a ball-and-socket joint, and so shaped 

 as to fit upon the rib, and at the other a finely-pointed 

 pencil (c). 



This lever is suspended at its central point by a pivot 

 (p), which permits of free movement up and down, but in 



