VOL. LXXXII.] PHILOSOPHICAL TKANSACTIONS. 143 



netic sensibility, he ventured to propose this kind of suspension, as being well 

 adapted to experiments requiring the needle to move with the least resistance. 



Exper. 1. From the great tenuity of a spider's thread, it might be expected 

 that it would bear very much twisting, without causing the needle to be sensibly 

 drawn from its magnetic meridian; but to prove it more fully by direct experi- 

 ments, Mr. B. first fastened a small hair to the side of the glass in which the 

 needle was suspended, and placed it so that the point of the needle stood exactly 

 opposite to the point of the hair. He then turned the needle round, by means 

 of a magnet, about 800 times, and on removing the magnet, the needle rested 

 exactly opposite to the hair: thus a spider's thread only 2 inches long, by twisting 

 800 times, did not cause any sensible deviation. 



Exper. 2. A fine harpsichord wire, 3 inches long, was suspended in a larger 

 glass. This wire was previously rendered magnetic by making it red-hot in the 

 flame of a candle, and suffering it to cool in the direction of the magnetic meri- 

 dian : by which it acquired polarity by the influence of the earth's magnetic at- 

 mosphere alone, and being soft, it possessed but a weak directive power. The 

 spider's thread was 3 inches long, and a small hair was fastened by varnish to the 

 north pole of this wire, which served more accurately to distinguish its position 

 opposite to a bit of ivory marked with degrees. This wire was turned round as 

 before, more than 1000 times; yet when suffered to rest, it stood exactly at the 

 same degree, the twist of the spider's thread having produced no sensible deviation. 



Exper. 3. A fine spider's thread was fastened to the spindle of a wheel used 

 for spinning flax; the wheel was placed so that the spindle and thread might hang 

 perpendicularly. To the end of the thread, which was about 2J- inches long, 

 was fastened, by its smaller end, one fibre of the feather of a goose-quill; the 

 lower end of the fibre rested on a book. The wheel was turned round till the 

 spindle had made above 18,000 revolutions. During this time the spider's thread 

 gradually became about 1 inch shorter; yet all this twisting did not cause the 

 fibre to turn round when raised from the book. On turning the spindle about 

 500 times more, the thread broke, apparently by twisting. 



Exper. 4. A bristle was suspended horizontally by a spider's thread somewhat 

 stronger than the last, and after turning the wheel till it produced 4800 revolu- 

 tions, it shortened the thread from 3 inches to 1 inch ; yet either end of the 

 bristle would move towards any warm substance which was presented to it, either 

 with or against the direction of the twist. 



Exper. 5. Several other light substances were suspended by fine spider's threads, 

 and placed in a cylindrical glass about 2 inches in diameter, as the thinnest part 

 of the wing of a dragon fly, thistle down, and the down of dandelion; of these, 

 the last appeared most sensible to the influence of heat, for when this down was 

 fastened to one end of a fine gold wiire suspended horizontally, or to one end of 



