100 Prof. R. Shida on a neiv Instrument for recording the 



How these electrical circuits are exactly arranged will be 

 seen later on with reference to the diagrams of the actual 

 instrument. At present it suffices to explain how the coil or 

 needle closes each electrical circuit separately, and without its 

 motion being being checked or impeded. This is effected by 

 taking advantage of one of the well-known properties of 

 matter, " surface-tension of liquids." When a capillary tube 

 is partly immersed in a liquid which wets the tube, like water, 

 the liquid ascends in the tube, and the smaller the diameter 

 of the tube the greater the height to which the liquid ascends, 

 and vice versa. In fact, it can be shown that if be the angle 

 of capillarity, r the radius of the tube, w the weight of unit 

 volume of the liquid, T the surface-tension per unit length of 

 the liquid in contact with air, then h, the height to which the 

 liquid rises, is 



1 2Tcos<9 



h= 



r w 



But the liquid is drawn up in the same way in the space 



between two parallel plates. In this case, if dbe the distance 



between two plates, then 



, 1 2Tcos0 



h~- . ; 



a w 



which shows that the height to which a liquid rises between 

 two parallel plates is equal to the height to which it rises in 

 a tube whose radius is equal to the distance between the 

 plates. 



Imagine now that there is a large number of capillary 

 arrangements, each consisting of two very narrow plates 

 standing in a vessel containing water at small distances from 

 one another, and arranged in an arc of a circle, while the 

 needle of the galvanometer is disposed in such a manner that, 

 as it turns round, it successively comes in contact with the 

 column of water drawn up between the plates of each of those 

 capillary arrangements and thus closes several circuits in 

 order; or else, that there is one such capillary arrangement, 

 while the needle carries a large number of points so disposed 

 that, when it turns round, these points successively come in 

 contact with the column of water in the capillary arrange- 

 ment, and thus close several circuits in order. Either of 

 these arrangements affords us the means of closing each 

 circuit separately, and without the motion of the needle being 

 checked. In the new instrument the latter plan is used, as 

 will be more clearly seen with reference to the diagrams 

 (Plates II. and III.). 



Having now explained briefly the principles upon which 



