ORDINARY MEETINGS. XXXl 
observations was made with the same cord and the same arrangements 
as the first. This series had to be made somewhat hurriedly, as will be 
seen by the dates of the individual experiments, but the experiments 
were made with the same care as those of the first series. It will be 
seen from the above table that (1) the treatment to which the cord had 
been subjected in the first series had diminished its rigidity, the values 
being smaller throughout than in the first series, and (2) that the initial 
diminution of rigidity with increase of tension, its final increment with 
tension, and the occurrence of a minimum point are as marked in the 
second series as in the first. 
To find out if the occurrence of the minimum point was due to the 
defective character of the attachments at the ends of the cord, Mr. 
Macdonald made a number of observations with new modes of attach- 
ment. These consisted of brass tubes in one end of which three 
longitudinal cuts had been made, the ends of the three strips thus 
formed being bent inwards and provided with teeth. The ends of 
the cord having been passed into these tubes, the strips were firmly bound 
to the cord by means of wire. Unfortunately Mr. Macdonald had not. 
sufficient time to make more than rough observations with the new 
arrangement. Such observations as he was able to make seemed to show 
that the minimum point had disappeared. Whether its disappearance 
was due to the more satisfactory attachments, the passing away of the 
heating effect or the fatigue of the cord, Mr. Macdonald hopes to deter- 
mine by further experiments. 
The above values of the rigidity agree fairly well with Mallock’s! 
determinations, Mallock having found that the rigidity of what he calls 
“soft grey ” india-rubber, determined dynamically, ranged from 5.52 to 
8.76, if expressed as in the above table, and that for ‘‘ hard grey” rubber 
it ranged from 10.77 to 13.94. Mr. Macdonald’s rubber could not be 
designated as either soft or hard; and his values are intermediate 
between Mallock’s for the soft and the hard specimens. 
The volume of the cord underwent very little change during either 
the first or the second series. In both series, however, there is an 
unmistakeable though small increase of volume with stretching ; but 
whether it was due to the stretching or to the series of oscillations to 
which the cord had been subjected does not of course appear. 
1 Proc. R. S. Lond., 46, 233, 1889, 
