18 



equation given by the pendulum experiments, the mean specific gra- 

 vity of the earth is found to be 6*566. Adverting to the excess of 

 this number above those given by the Schehallien and the Torsion- 

 rod experiments, the author remarks that it is very difficult to assign 

 the causes or the measures of error in either of the experiments, but 

 expresses his belief that the result of the present experiment may 

 compete on at least equal terms with the others. 



A paper was also read, entitled " A Description of a new 

 Sphygmoscope, an Instrument for indicating the Move- 

 ments of the Heart and Blood-vessels with an Account of 

 Observations obtained by the aid of that Instrument." By 

 S. SCOTT ALISON, M.D., Licentiate of the Royal College 

 of Physicians, London. Communicated by G. 0. REES, 

 M.D., F.R.S. Received January 12, 1856. 



The sphygmoscope (fig. 1) consists of a small chamber containing 

 spirits of wine or other liquid, provided with a thin india-rubber 

 wall, where it is to be applied to the chest. At the opposite extre- 

 mity the chamber communicates with a glass tube, which rises to some 

 height above the level of the chamber. Liquid is supplied to the 

 .instrument until it stands in the tube a little above the level of the 

 chamber. The pressure of the column of liquid in the tube acts 

 upon the elastic or yielding wall of india-rubber and causes it to pro- 

 trude. This protruding part or chest-piece is very readily affected 

 by external impulse ; it yields to the slightest touch, and being 

 pushed inwards, causes a displacement of the liquid in the non-elastic 

 chamber, and forces a portion of liquid up the tube. The protruding 

 wall of india-rubber is driven inwards when it is brought in contact 

 with that portion of the chest which is struck by the apex of the 

 heart, and a rise in the tube takes place. When the heart retires, 

 the india-rubber wall, affected by the pressure of the column of 

 liquid in the tube, is pressed back, follows the chest, and permits 

 the liquid to descend. The degree to which the india-rubber wall is 

 forced in by the apex of the heart is denoted by a corresponding 

 rise in the tube, and the amount of protrusion of the india-rubber 



