280 ON THE RFGIDITY 



nearly as possible, in both. In the static determinations of this, 

 and of all subsequent series, Mallock's mode of applying the 

 twisting force was used. The kinetic observations were made 

 with different amplitudes of angle of oscillation, and the static 

 observations with different angles of torsion. The general 

 procedure was as in the former case. Table II contains the 

 results. 



In none of the columns of rigidity values of this table 

 do the values found indicate any simple law of variation with 

 tension. They do not even increase or decrease continuously as 

 tension increases, but appear to oscillate between increment and 

 decrement, and by amounts which are not accounted for merely 

 by errors of observation. The variations cannot be accounted 

 for even by errors of method, because in general both methods 

 give similar variations. They may, perhaps, be partially at 

 least, accounted for by defective procedure. Nevertheless, two 

 conclusions may be drawn : (1) The smaller the angle of 

 torsion in the static determinations and the angle of oscillation 

 in the kinetic determinations, the greater is the value of the 

 rigidity obtained. Mallock drew the same conclusion as to 

 kinetic rigidities from his observations. (2) The kinetic 

 determinations show a point of minimum rigidity as tension 

 increases ; but the static determinations are not sufficiently 

 exact to be decisive as to whether or not the existence of this 

 point is independent of the method. Thus the kinetic observa- 

 tions bear out Mr. Macdonald's result that the kinetic rigidity 

 exhibits the minimum puint in the case of a cord previously 

 unstretched. 



The cord used in the last experiment being now in a state of 

 tension, was experimented on in a reverse manner. It was left 

 a day under the full load, when its rigidity was determined. 

 Then one of the weights was taken off, and it was again left for 

 a day under the diminished load, and its rigidity determined > 

 and so on. 



