DE. JOULE ON SOME THEEMO-DTNAMilC PEOPEETIES OF SOLIDS, 
103 
additions and removals of water, which was kept well mixed by a current of bubbles 
of air blown from time to time .through a narrow tube into the lower end. The positions 
of the pins, showing the length of the rubber, were ascertained by means of a graduated 
scale placed behind the tube, viewed through a telescope which was raised or depressed 
according to the level of the pins. 
38. In my first experiment the stretching weight, inclusive of the weight of the tube, 
was 3 lbs., and the water in the tube being adjusted to 7 ° Cent., the length of the thong 
between the pins was 1'026 inch. The temperature of the water was then raised to 17°, 
and kept there for ten minutes, when the length was found to be reduced to 0'964 inch. 
A third observation at 28° gave the length 0-9. It was evident that this contraction 
was partly owing to the recovery by heat of the rubber from the constrained state in 
which it was left by the experiments of the preceding Table ; for the lengths observed 
on lowering the temperature successively to 16°‘6 and 7°'4, namely, 0-91 and 0-922, 
indicated a lengthening effect from the application of cold, only one quarter of the 
amount of the previous shortening by heat. I now used a stretching weight of 6 lbs., 
which immediately increased the length to 1-22, and in the course of thirty-six hours 
further increased it to 2-548 inches at the temperature 5°-4. Raising the temperature 
successively to 12° and 17°, the length was diminished to 2-627 and 2-459. Then on 
depressing it to 9°-6 and 4°-3, I observed 2-476 and 2-490. After leaving the same 
weight on for five hours longer, I observed lengths of 2-559, 2-514, and 2-47 with the 
temperatures 6°-2, 12°-4, and 20°-2, and 2-483 and 2-498 at temperatures successively 
depressed to 12° and 5°. After the lapse of twenty-two hours more, I found the lengths 
2-624, 2-568, and 2-51 at the temperatures 6°-2, 13°-6, and 22°; and 2-523 and 2-548 on 
depressing the temperature to 13° and 6°-4. All these observations show the gradual 
elongation effected by tension, the tendency of heat to restore the original length, and 
the increase or decrease of elastic force with the elevation or depression of the tempera- 
ture of the rubber, 
39. I now reduced the stretching weight to 1 lb,, being that of the tube and the 
water contained by it. The observed length was 1-63, and in forty-five minutes further 
decreased to 1-621, Afterwards it began to increase gradually; in five hours attaining 
to 1-635, in seventeen more to 1-724, and after a further lapse of forty hours to 1-751. 
These observations were at 7°-l. Then raising the temperature to 21°-6, the length was 
reduced to 1-191; and on depressing it again to 7°-4, the length was further reduced to 
1-181. Keeping the rubber at the same temperature it still continued to contract, and 
in two hours its length was only 1-17. Then on raising the temperature to 23°, and 
afterwards depressing it to 7°-2, the length was successively reduced to 1-161 and 1-141, 
These and similar observations were continued for several days with like results, confirm- 
ing my previous remarks, and also developing the curious fact, that when a piece of india^ 
rubber, which has been previously gradually lengthened by stretching, is shortened by 
the temporary application of heat, the shortening effect continues to go on for somq time, 
even if the rubber has been reduced to its previous temperature. 
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