112 
MR. A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 
the resistance to motion in the directions 0 y and Oz is great, the disturbance of 
the equilibrium of the suspended system, due to these forces, may be neglected. 
The method of measuring the force X, or rather the method of comparing X for 
different substances, is shown in fig. 2. The torsion arm, ABCD, is made of 
aluminium. The angle through which the torsion arm was twisted when the 
magnetic field was excited was measured by the double suspension mirror DME. 
The dash-pot P contained a mixture of paraffin-oil and heavy mineral oil in which 
PI a n 
four vanes, V, hung. The arm EF is the extremity of a three-dimensional 
adjustment stage. The brass case S, which surrounded the torsion arm and 
suspension mirror, was rigidly attached to a brass carrier which was provided with a 
screw motion and slid upon rails. These rails were screwed to a heavy slate bed 
which was supported by two large blocks of stone. To prevent the transmission of 
vibrations to the suspended system from outside, two layers of indiarubber were 
inserted between the stone blocks and the slate bed. The rod GH provided with 
the cranks, C x and C 2 , was used to rest the torsion arm while the substance under 
investigation was being attached to the end A (see plan and end elevation). To 
preserve balance of the torsion arm when different masses of substance were used, a 
rider R was provided which could be moved by the rod L into different positions along 
the torsion arm. A very fine phosphor-bronze wire, attached to the projection B, 
suspended the movable parts of the system. 
