615 
With a silver wire of 10 cm. length and of a diameter of more 
than 10.8 u the sensitiveness is mainly limited by the elasticity ; 
with silver wires of the same length but thinner than 10.8 u, the 
weight of the wire is the most serious obstacle to increasing the 
sensitiveness of the instrument. With a wire of 21.6 u the elasticity 
is 4 times more important as a limiting factor than gravity. 
If the influence of the two limiting factors is taken together, we 
find for the deflection of the middle part of the string: 
TA 
6d Ez 
Des 
fp, = 
(5) 
‘/,a yg + 
if the string be totally relaxed and fixed on the support without 
any longitudinal or torsional tension. 
With this formula we can calculate the next table giving the 
deflection of a 10 em. string of 1 u in a field of 10.000 Gausses 
with a current of 10-1? Ampere and an enlargement of 1000 times. 
TABLE II. 
Copper | 0.72 mm 
Silver 0.62 » 
Gold | 0.34 » 
Aluminium | 2.20 » 
Platinum | 0.33 » 
Silvered quartz | Lakh >> 
In the same way I find for an aluminium string of 2 u and 56 
mm. length in a field of 18000 gausses a theoretical deflection of 
„57 mm., the magnification being 1000 fold. In my former commu- 
nication I stated that such a string had given me a deflection of 
.40 mm. If we had taken the elasticity as the limiting agent we 
ought to have expected a deflection of 1.20 mm. 
Doubtless we get a better approximation for the liminal sensitiveness 
of the string galvanometer by considering the influence of the weight 
of the string without neglecting its elasticity. 
