220 Dr. J. Wilsing on the Application of the Pendulum to 
tive enough to be appreciably influenced by smaller masses 
which are capable of accurate determination. 
The necessary degree of sensitiveness may be obtained by 
adjusting the centre of gravity of the pendulum close under 
the axis of oscillation. With an experimental apparatus, which 
was intended to get some indications as to the practical execu- 
tion of this modification, experiments were made in September 
of last year in the observatory. ‘This consisted of a prismatic 
rod of thin sheet-iron, at the ends of which were fixed lead 
balls, each weighing 300 grammes. The steel knife-edge, 
which worked on agate, was fixed in the middle of the 
rod. The apparatus was so arranged that, when in equilibrium, 
its axis was almost vertical. The motion was read off by 
reflection. When the position of equilibrium was found and 
the attracting masses were placed near the lead spheres, from 
the deflection of the pendulum, the ratio of their attraction to 
the constant of gravitation can be determined. By reversing 
the direction of the deflecting forces, the action of the force 
can be doubled. 
This method may be regarded as a combination of the two 
oldest methods. In comparison with the method used by 
Prof. von Jolly with such distinguished success, it has the 
advantage that the sensitiveness of the pendulum is consider- 
ably greater. 
Although the crude construction of the experimental instru- 
ment made it very difficult to introduce the needful corrections, 
—it being mounted on a wooden support, and not sufficiently 
protected against currents of air,—a time of oscillation of 150 
seconds could be attained without the occurrence of irregula- 
rities which could be regarded as essential. This may be 
explained by the fact that partial oscillations are excluded 
as completely as possible, and the axis of the pendulum de- 
flects but a little on each side of the vertical, so that the 
bending of the rod is only a very slight amount. The degree 
of delicacy corresponding to the above-mentioned time of 
oscillation would be sufficient to measure the attraction of 
spheres of a few hundredweight, as is possible by using a 
torsion-balance. 
The sensitiveness of the apparatus was ascertained from the 
observation of oscillation by the addition of weights, which 
were placed at known distances from the knife-edge at the 
lower end of the pendulum. If gm is the weight of the piece 
added, d the distance of its centre of gravity from the knife- 
edge, the time of vibration for infinitely small oscillations is 
Gap MK? + mk? + md? 
g( Ms + md) 
