Mr. F. Guthrie on Approach caused by Vibration. 353 



will be at hand for the approach of the cardboard to the 

 fork. 



§ 30. Experiment 11. — A "Cartesian diver" was made out 

 of a test-tube, a bubble of air. and a beaker-glass of water. This 

 was so nicely adjusted that it rose when near the surface of the 

 water, and sank when the top of the tube was # 05 metre below 

 the surface. When resting on the bottom of the beaker, the top 

 of the test-tube was below the surface of the water. When the 

 diver was resting on the bottom of the beaker, the tuning-fork 

 A in a state of vibration was presented to the glass in various 

 directions with regard to the tube. The fork was placed some- 

 times in contact with the water, sometimes in the neighbouring 

 air, and sometimes in contact (towards the base of the fork) with 

 the glass. Although the vibration of the bottom of the beaker 

 caused the diver to leap up, it invariably sank again and showed 

 no sign of undergoing any alteration in specific gravity. If, now, 

 the question in § 29 were answerable in the negative, the 

 equilibrium would have been destroyed, because the atmospheric 

 pressure on the one hand, and the elasticity of the confined air 

 on the other being equal and opposite forces, an alteration in 

 one, caused by its subjection to successive sonorous waves, would 

 have altered the volume of the confined air and so destroyed the 

 equilibrium. 



§ 31. I hoped to throw light upon the fundamental experi- 

 ments of §§ 1 and 21 by varying the nature of the surface of 

 the body which received the vibrations, with the view on the one 

 hand of preserving them, and on the other of dispersing them 

 as much as possible. With this view Experiments 12 to 15 

 were undertaken. 



§ 32. Experiment 12 (fig. 11). — Upon one end of a splinter 

 of wood 0*5 metre long, a cylinder of cardboard 0*03 metre in 

 diameter and 0*04 metre deep, closed at the bottom, was fastened 

 in such a manner that its axis was horizontal and its bottom in 

 the plane V. The cylinder was counterpoised, and the whole 

 was hung from an unspun silk thread. The vibrating fork A 

 was brought near the open end of the cylinder in the three po- 

 sitions already described, and also with one prong inserted into 

 and nearly touching the bottom of the cylinder. In all cases 

 motion towards the fork ensued. 



§ 33. Experiment 13. — A handful of cotton-wool was hung 

 upon the splinter in place of the cylinder of Experiment 12. 

 The cotton moved towards the fork from a distance of at least 

 0*05 metre, when the latter was presented to it in either of the 

 three positions, § 6. 



Muslin and washleather behaved in a similar manner. 



§ 34. Experiment 14. — A paper circular drum, 0*25 metre in 



