20 THE ROYAL SOCIETY OF CANADA 
2. Determination of the Isothermal Young’s Modulus. 
The statical method used depends on observing the depression 
produced at the centre of a bar, supported on two knife-edges, when a 
known weight is added at the centre of the bar. The depression was 
found by a method, due to Konig, illustrated in the figure below. 
The rod rests on two knife-edges, K, and K,, and mirrors, which 
are at right angles to the rod, are rigidly attached to it. The vertical 
scale § is reflected first from the mirror M, then from M, and read 
through the telescope F. The weight is applied at a knife-edge which 
is Just midway between the knife-edges K, and K,. On looking through 
the telescope we see one division on the scale coinciding with the cross 
hair of the telescope; on loading the beam another division of the scale 
will come on the cross hair, and by measuring the distance between 
these divisions we can determine the angle @ through which each free 
extremity of the bar has been bent. If d, is the distance between the 
mirrors, D the distance of the scale S from the mirror M,, and v the 
total alteration in the scale reading, 
