Physics. — “The Limit of Sensitiveness of the String-galvanometer’’. 
(2¢ communication). By Prof. J. K. A. WERTHEIM SALOMONSON. 
(Communicated at the meeting of June 26, 1920). 
In the meeting of June 26th 1918 I read a paper in which I showed, 
that the sensitiveness of the Einthoven-galvanometer was limited by 
the elasticity of the material of the string. At the same time I stated 
that the actual limit was never reached. The theoretical liminal 
value in every case was much smaller than the actually observed 
value, except with very thick strings. There seems to exist a simple 
cause for this fact. It is not only the elasticity of the perfectly 
velaxed string that causes the deviated string to resume its original 
form and position of rest after stopping the current through it, but 
also gravity. As the exact form of a deviating totally slackened 
string is not the same in every case, and cannot be exactly repre- 
sented by a formula, it is only possible to approximately calculate 
the influence of gravity. We can do this in the simplest way by 
assuming that the string is suspended in a homogeneous field of H 
gausses; that it bends in the point of suspension without any resi- 
stance or friction; that the lower current bearing connection is 
equally free from resistance, friction and mass; and finally that the 
string is straight and rigid and does not change its form. If the 
length of the string be /, the diameter d, the density of its material 
y and the gravitational constant g, the string is acted upon by a 
force p='/, 2d? lyg. As soon as the wire be deflected, its middle 
part being moved over a distance h, the force pulling the string 
back to its original position is 
psta@lyy Shad yhg , Perey s(t) 
If this force is in equilibrium with the current 2, we may put: 
Hl= tx diya 
or 
(gpa ad : (2) 
bad'yg 
In my former communication I found the formula: 
Fils 
n= -— (3) 
62 Ed* 
