PHENOMENA OF SUCTION. 313 



next instant have to fill the space within the ring 3, in 

 the next that within the ring 5, and so on. Now the 

 areas of the circles drawn in fig. 204 -B, with radii of 

 1,2, 3,4, and 5 cm , are 1 x 1 x 3-14,2 x 2 x 3*14, etc., 

 or 3-14, 12-56, 28'26, 50'24, and 78'50 square centi- 

 metres, and the areas of the successive rings between 

 the circles are 



12-56 - 3-14 = 9-42 = 3 x 3'14 



28-26 - 12-56 = 15-70 = 5 x 3*14 



50-24 - 28-26 = 21-98 = 7 x 3-14 



78-50 - 50-24 = 28-26 = 9 x 3-14 



If the particles of air are to maintain their original 



velocity, it is necessary that the quantity of air which 



it a certain time fills the inner circle of 1 x 3*14 



square centimetres area, should fill at the following 



nstant, the ring of 3 x 314, at the next instant the 



ing of 5 x 3*14 centimetres area, and so on : that is, 



he same quantity of air must successively fill a space 



, 5, 7, 9 times as great as at first, and must hence 



[iminish its density and consequently its pressure so as 



o become from ^ to ^ of what it was in the centre of 



he circle. The pressure of the air which passes 



brough the tube into the space between the discs is 



aus, although originally greater than the pressure of 



le atmosphere, gradually becoming less while radiating 



), and escaping at the edge, and becomes actually less 



mn the atmospheric pressure. It is true, that the 



alocity of the air particles decreases from the centre to 



ie edge, and the diminution of pressure is not quite so 



;eat as would appear from our calculation, because the 



sternal air opposes a considerable resistance to the 



