3G Mr. F. Guthrie on Approach caused by Vibration. 



The tuning-fork which was most employed, and Fig. 1, 

 which I call fork A, gave 128 complete vibrations per 

 second, and had the following dimensions : — 



metre. 

 oy = 0'0230, 

 o,r=0-0172, 

 o^=0'3255. 



I call the three faces intersecting in o, the faces a, b, 

 and c respectively. Let the symbol H c , &c. denote 

 the position of the fork when the face c is horizontal, 

 &c. 



§ 5. Experiment 1. — The fork A was set vibrating by drawing the bow 

 across the edge oy ; the plane of vibration was accordingly parallel to b. 

 The fork was then brought into the neighbourhood of an ascending thread 

 of smoke. The fork and smoke had in succession the three relative posi- 

 tions : — 



(1) H 



(2) H 



(3) H 



Fig. 2. 

 1 



i. 



The smoke passed across the face a parallel to oy. 

 The smoke passed across the face b parallel to ox. 

 The smoke passed across the face c parallel to ox. 

 In all cases the smoke clung to the surface across which it passed as 

 though the fork were at rest. 



§ 6. Experiment 2. — A cylindrical 

 glass tube T, 0*4 m. long and 0*042 m. 

 in internal diameter, was fastened (fig. 2) 

 in a horizontal position. One end was left 

 open, the other carried a cork, through 

 the centre of which passed a horizontal 

 tube t, 0*04 m. long and 0*0035 m. in- 

 ternal diameter. These tubes were rilled 

 with smoke, and the fork A, which had 

 been set vibrating as in § 5, was brought 

 to the open end of the wide tube. The 

 fork and tube had in succession the 

 four relative positions shown in fig. 2, 

 namely : — 



(1) H c . Axis of tube perpendicular 

 to a. 



(2) II 6 ,. Axis of tube perpendicular 

 to b. 



(3) IT a or H 6 . Axis of tube perpendicular to c. 



(4) The same as (3), but having one prong of the fork thrust as far 

 as possible into the tube T. In none of the cases did the smoke show any 

 tendency to escape through the tube t, nor was fresh air drawn in. 



§ 7. Experiment 3.— The cork and tube t of experiment 2 were with- 



4. 



