148 Dr. Young's Experiments and Inquiries 



tions with an aperture .15 in diameter opposed to the stream; 

 C with .3 ; and D with .5. 



Figs. 2 1 — 23. A, the half section of a current from a tube .3 

 in diameter, with a pressure of .5, of 1, and of 3. B shows the 

 course of a portion next the axis of the current, equal in dia- 

 meter to those represented by the last figures. 



Plate IV. 



Fig. 24. The appearance of a stream of smoke forced very 

 gently from a fine tube. Fig. 25 and 26, the same appearance 

 when the pressure is gradually increased. 



Fig. 27. See Section III. 



Fig. 28. The perpendicular lines over each division of the 

 horizontal line show, by their length and distance from that 

 line, the extent of pressure capable of producing, from the re- 

 spective pipes, the harmonic notes indicated by the figures placed 

 opposite the beginning of each, according to the scale of 22 

 inches parallel to them. The larger numbers, opposite the middle 

 of each of these lines, show the number of vibrations of the cor- 

 responding sound in a second. 



Plate V. 



Figs. 29 — 33. See Section X. 



Fig. 34,. The combination of two equal sounds constituting the 

 interval of an octave, supposing the progress and regress of 

 the particles of air equable. Figs. 35, 36, 37, a similar repre- 

 sentation of a major third, major tone, and minor sixth. 



Fig. 38. A fourth, tempered about two commas. 



Fig. 39. A vibration of a similar nature, combined with subor- 

 dinate vibrations of the same kind in the ratios of 3, 5, and 7. 



