492 Mr. J. H. Gray on the 



In the Proceedings of the Royal Society for 18*89, 

 page 291**, an account is given of some very interesting 

 tests made of the value of the torsional rigidity of spider's 

 thread by Professor A. Tanakadate, of Japan. He found that 

 the torsional rigidity is rather less than one sixth of that of 

 silk fibre of the same thickness. 



For the tests about to be described, several garden spiders, 

 species Epeira Diadema, about one eighth of an inch in length 

 of body, were caught and placed each in a separate box. 

 Fresh threads, free from dust, could thus be obtained. If 

 more than one spider was placed in the same box the number 

 soon became reduced to one, the others having been killed 

 and eaten by the survivor. It is necessary to employ the 

 garden spider, as the house species, which makes a closely 

 woven web quite different from the beautiful spiral of the 

 Diadema, cannot be made to spin a thread. The spinner 

 was taken out of its box and placed on a card or piece of 

 wood held about three feet or so above the ground. A slight 

 tap was sufficient to cause the spider to drop from the support, 

 spinning a thread as it fell. Sometimes it dropped to the 

 floor, but in most cases it stopped when it had fallen six or 

 eight inches, and, after hanging apparently motionless for a 

 second or two, rapidly threw out an exceedingly light thread 

 which floated outwards and upwards in the direction of the 

 slightest draught. In the space of ten seconds sometimes as 

 many as ten feet of thread were thrown out. If the outer end 

 of this thread happened to attach itself to one of the adjacent 

 supports, the spider immediately endeavoured to make its 

 escape. The threads thus spun were exceedingly thin, and 

 could only be seen when a strong light was thrown upon 

 them and with a black background. 



While it was still floating, two marks were made about 

 50 centimetres apart, by carefully fixing with gum two pieces 

 of the thread, each 3 millimetres long, at right angles to the 

 length* Small wire weights from ^ to 30 milligrammes were 

 made, and half a milligramme was fixed a little beyond the 

 furthest thread-mark. This was sufficient to bring the thread 

 down to the vertical without appreciably stretching it. On a 

 vertical stand were fixed two paper scales graduated in half- 

 millimetre divisions, the one scale about 50 centimetres above 

 the other. Directly in front of these scales the thread was 

 hung, and by means of a telescope placed six feet away the 

 readings corresponding to the two marks on the thread were 

 obtained. Precautions were taken to prevent draughts, as 



* "Note on the Thermoelectric Position of Platinoid/' by J. T. Bot- 

 tomley, M.A., F.R.S., and A. Tanakadate. 



