VOL. XC.] 



PHILOSOPHICAL TRANSACTIONS. 



605 



pressure ; and that the ratio of the expenditures by different apertures, with the 

 same pressure, lay between the ratio of their diameters and that of their areas. 

 The 2d, 3d, and 4th tables show the result of similar experiments, made with 

 some variations in the apparatus. It may be inferred, from comparing the ex- 

 periments on a tube with those on a simple perforation, that the expenditure is in- 

 creased, as in water, by the application of a short pipe. 



a is the area, in square inches of an aperture 

 nearly circular, b, the pressure in inches, c, 

 the number of cubic inches discharged in one 

 minute. 



All numbers throughout this paper, where the 

 contrary is not expressed, are to be understood of 

 inches, linear, square, or cubic. 



a is the area of the section of a tube about 

 2 inches long, b, the pressure, c, the quan- 

 tity of air discharged in a minute by estimation. 



a is the area of the section of a tube. 

 b, its length, c, the pressure, d, the 

 discharge in a minute. 



a is the area of an oval aperture, formed by flat- 

 tening a glass tube at the end: its diameters were 

 .025 and .152. b, the pressure, c, the discharge. 

 2. Of the direction and velocity of a stream of air. — An apparatus was contrived 

 for measuring, by means of a water-gage communicating with a reservoir of air, 

 the pressure by which a current was forced from the reservoir through a cylindrical 

 tube; and the gage was so sensible that, a regular blast being supplied from the 

 lungs, it showed the slight variation produced by every pulsation of the heart. 

 The current of air issuing from the tube was directed downwards, on a white plate, 

 on which a scale of equal parts was engraved, and which was thinly covered with 

 a coloured liquid ; the breadth of the surface of the plate laid bare was observed at 

 different distances from the tube, and with different degrees of pressure, gare being 

 taken that the liquid should be so shallow as to yield to the slightest impression of 

 air. The results are collected in tables 5 and 6, and are exhibited to the eye in 

 plate 9, figs. 1 to 12. To measure with greater certainty and precision, the velo- 

 city of every part of the current, a 2d cavity, furnished with a gage, was provided, 

 and pieces perforated with apertures of different sizes were adapted to its orifice: 

 the axis of the current was directed as accurately as possible to the centres of these 

 apertures, and the result of the experiments, with various pressures and distances, 

 are inserted in tables 7, 8, 9. The velocity of a stream being, both according to 

 the commonly received opinion and to the experiments already related, nearly in 

 the subduplicate ratio of the pressure occasioning it, it was inferred, that an equal 



.003 



Table 4. 



B 



.28. 



46.8 



