NOVUM ORGANUM 235 



not be passed over, not relating to progressive but spherical 

 motion that is, the expansion of bodies into a greater, or 

 their contraction into a lesser sphere. For in our measure 

 of this motion we must inquire what degree of compression 

 or extension bodies easily and readily admit of, accord 

 ing to their nature, and at what point they begin to resist 

 it, so as at last to bear it no further as when an inflated 

 bladder is compressed, it allows a certain compression of 

 the air, but if this be increased, the air does not suffer 

 it, and the bladder is burst. 



We have proved this by a more delicate experiment. 

 We took a metal bell, of a light and thin sort, such as is 

 used for salt-cellars, and immersed it in a basin of water, 

 so as to carry the air contained in its interior down with it 

 to the bottom of the basin. We had first, however, placed 

 a small globe at the bottom of the basin, over which we 

 placed the bell. The result was, that if the globe were 

 small compared with the interior of the bell, the air would 

 contract itself, and be compressed without being forced out, 

 but if it were too large for the air readily to yield to it, 

 the latter became impatient of the pressure, raised the bell 

 partly up, and ascended in bubbles. 



To prove, also, the extension (as well as the compres 

 sion) which air admits of, we adopted the following method: 

 We took a glass egg, with a small hole at one end; we 

 drew out the air by violent suction at this hole, and then 

 closed the hole with the finger, immersed the egg in water, 

 and then removed the finger. The air being constrained by 

 the effort made in suction, and dilated beyond its natural 

 state, and therefore striving to recover and contract itself 

 (so that if the egg had not been immersed in water, it would 

 have drawn in the air with a hissing sound), now drew in 



