386 Prof. Tyndall on the Action of Sonorous 



whose notes, written last June, I make the following ex- 

 tract : — i 



" From many experiments made with care the following facts 

 were obtained : — 



" 1. A jet of air rendered visible by suspended particles of 

 chloride of ammonium, when moving slowly, leaves the orifice 

 from which it is forced as a slender stream of the diameter of 

 the orifice, and of equal thickness throughout a length of from 

 6 to 12 inches. It then spreads out in an inverted cone. When 

 at a higher velocity the apex of the cone approaches the orifice, 

 but maintains the same angular opening. At the greatest 

 velocity the cone is formed almost immediately as the smoke 

 leaves the orifice. 



"2. The appearances of a jet of air are in all respects the 

 same as those of a jet of steam. 



" 3. When a tuning-fork is held near to this stream it causes 

 the cone to appear where it is held, thus instantly reducing the 

 height of the stream. If held near the orifice the cone is no 

 longer one, but is split into two, and each of the two streams 

 issuing from the central stream is seen to possess a kind of 

 involving motion. 



" 4. The splitting of the jet depends on the velocity of the 

 current in relation to the pitch of the fork. 



"5. With a very low velocity, giving a long parallel line ot 

 smoke, Ut 4 will not divide the column, but Ut 3 will easily 

 do so. Increasing the velocity, the higher notes are all capable 

 of splitting the stream, whilst the lower notes lose their power. 



" 6. At a certain velocity the issuing air often is heard to 

 sound. When this takes place, the column of air is seen to be 

 feebly bifurcated near its root. A tuning-fork in unison with 

 the note (Ut 3 or Mi 3 ) augments the intensity with which 

 the streams diverge. The angle of divergence in all cases re- 

 mains about the same, viz. about 60°. 



" 7. By tapping the table or support of the jet, the smoke is 

 caused to issue in pulses, giving the smoke as it rolls away a 

 most beautifully crimped appearance. 



" 8, The jet of smoke can be best seen by reflecting the sun- 

 light on it, and shielding the eyes from the direct glare. 



"9. The image of the jet, single and bifurcated, can be dis- 

 tinctly seen by its shadow, and can be cast on a screen by a short- 

 focus lens. 



" 10. The bifurcation occurs in the plane of the prongs of the 

 tuning-fork. This is invariably the case. 



"11. The stream is always easier to split near its root, and 

 sometimes can only be split there. 



" 12. When the jet is sounding, the stream of smoke is often 



