Prof. Thomson on the Electro-dynamic Properties of Metals, 393 



The rise in the instrument is greater in liquid than in aeriform 

 tumours on account of the compressibility of air, and the fall is more 

 rapid and decided when the contents of the tumour are liquid. 



For the most part, the hand-sphygmoscope is best applied simply 

 with the aid of the fingers. It is delicately held between the tips of 

 the thumb, fore- and middle-fingers, the nails resting on the examinee. 

 The elastic wall is on no account to be pressed down with a dead 

 weight upon the vessel. It is to be nicely lowered to the level of the 

 artery when collapsed. When the artery rises, it will strike the 

 elastic wall, and as the chamber is fixed by the fingers, the entire 

 blow is communicated to the liquid and it rises in the tube. During 

 the retirement or collapse of the artery, the elastic wall resumes its 

 level condition and draw* the liquid down the tube. This motion 

 of the liquid allows the instrument to be employed though the open 

 end of the tube be dependent. When it is desired to avoid the varying 

 pressure experienced when the instrument is held between the fingers, 

 some such apparatus as was invented by Dr. E. S. Blundell, or an 

 elastic band suitably applied around the wrist, will be useful. 



The sphygmoscope is for several purposes renderedmore convenient 

 of application by interposing, between the chamber and the glass tube, 

 a piece of india-rubber tube of suitable bore and length. In this 

 way the comparison of the beat of the heart and the pulse of an 

 artery is much facilitated, for the glass tubes of the two instruments 

 employed may be brought parallel and close to each other, so that 

 the opposite motions of the liquids in the two tubes are, by near 

 contrast, rendered easier of observation. In employing this adapta- 

 tion, care must of course be taken that the india-rubber tube is of 

 the same calibre and length in both instruments. 



It is hoped that the sphygmoscope will aid in the acquisition of 

 additional knowledge of the movements and condition of the heart, 

 the situation of which within a case of bone, wisely provided to secure 

 it from injury, has this disadvantage for the physiologist and phy- 

 sician, that the action and condition of the organ are with difiiculty 

 made out. By means of the sphygmoscope, that small amount ot 

 movement which is manifested at the exterior of the chest may be 

 rendered more appreciable to our senses, and more available for phy- 

 siological and curative purposes ; and perhaps information may be 

 obtained by this instrument which has hitherto been procurable only 

 by the practice of vivisection. 



Park Street, Grosvenor Square, London, 

 Jan. 12, 1856. 



Feb. 28.-- The Lord Wrottesley, President, in the Chair. 



The following communication was read : — 



The Bakerian Lecture. — " On the Electro-dynamic Properties of 

 Metals." By Professor William Thomson, F.R.S. 



The Lecturer gave an exposition of the substance of a paper pre- 

 sented by him to the Society under the above title. 



The paper consists of five parts, namely: — 1. On the Electric 

 Convection of Heat ; 2. On Thermo-electric Inversions ; 3. On 

 the Effects of Mechanical Strain and of Magnetization on the 

 Thermo-electric Qualities of Metals ; 4. On Methods for comparing 



PhiU Mag. S. 4. Vol, 12. No. 80. Nov, 1856. 2 D 



