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



cient ground would be at hand for the approach of the cardboard to the 

 fork. 



§21. Experiment 8. — 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 0*05 m. below the surface. When resting on the 

 bottom of the beaker, the top of the test-tube was 0'067 m. 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 

 sometimes 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 § 20 were answerable 

 in the negative, the equilibrium would have been destroyed, because the 

 atmosperic 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. 



§ 22. I hoped to throw light upon the fundamental experiment of § 1 

 and § 1 2, 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 expe- 

 riments 9-12 were undertaken. 



§ 23. Experiment 9, fig. 5. — Upon one end of a splinter Fig. 5. 

 of wood 0*5 m. long, a cylinder of cardboard 0'03 m. in 

 diameter and 0"04 m. 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 coun- 

 terpoised, 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 positions already de- 

 scribed, and also with one prong inserted into and nearly 

 touching the bottom of the cylinder. In all cases motion 

 towards the fork ensued. 



§ 24. Experiment 10. — A handful of cotton-wool was 

 hung upon the splinter in place of the cylinder of experi- 

 ment 12. The cotton- wool moved towards the fork from a 

 distance of at least 0*05 m., when the latter was presented 

 to it in either of the three positions, § 8. 



Muslin and washleather behaved in a similar manner. 



§25. Experiment 11. — A circular paper drum 0*25 m. in diameter 

 having a rim 0*025 m. deep, was hung by a silk tape in the same manner 

 as the cylinder of § 23. Parchment was stretched across the wide eud of 



