380 
MR. GEORGE W. WALKER ON 
which the “modulus” is given, and the range e = 56° to 90°, for which the values 
are real and for which there is a real reflected longitudinal wave as well as a real 
reflected transversal wave. 
These results are exhibited graphically in fig. 3, wherein A has been taken as 
numerically 1, and for convenience, the — sign has been disregarded. 
It is important to remember that the results we have obtained for reflexion of 
elastic disturbance are not confined to periodic waves (cf. Lord Kelvin, ‘ Phil. Mag.,’ 
