88 
MESSES. G. F. C. SEAKLE AND T. G. BEDFORD 
negative couples. The process of changing the load from + 300 to — 300 grammes 
and hack again vas continued till it appeared that the curves connecting Bq and 
vith the load had nearly settled down to a permament form. 
In the first experiments, when the permanent set was about 6 revolutions, the first 
ai^plication of a negative couple due to 200 grammes caused the wire to yield 
somewhat, and when the load of —300 grammes vms reached, the yielding was great 
enough to cause the wheel to turn gradually through half a revolution. In the 
next cycle of loading this effect of a negative couple was small, and it became 
much smaller for each successive cycle. With the large permanent sets of 20 and 50 
revolutions the wire Ijecame so hard that the yielding under a negative couple vas 
very small even in the first cycle. Tlie positive couples caused little yielding even in 
the first cycle with the permanent set of 6 revolutions. 
The observations were too numerous to be recorded, except in the form of the 
curves in figs. 15, 16. In order to shovr all the curves on a single diagram, we have 
taken a different position of the zero line for and W in each curve. 
Fig. 16. 
In these experiments it was found that after the first application of a negati^ e 
couple due to 300 grammes the iron had roughly reached a cyclic state, and thus, to 
avoid confusion, we give only U cycles as continuous curves. For a permanent set 
of 6 turns 3f cycles were actually gone through, and in each of the other cases 
