43* 



BACON 



traction 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, according to their nature, and at 

 what point they begin to resist it, so as at last to bear it no fur- 

 theras 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 bot- 

 tom 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 compression) 

 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 im- 

 mersed in water, it would have drawn in the air with a hissing 

 sound), now drew in a sufficient quantity of water to allow the 

 air to recover its former dimensions. 



It is well ascertained that rare bodies (such as *Ir) admit of 

 considerable contraction, as has been before observed; but 

 tangible bodies (such as water) admit of it much less readily, 

 and to a less extent. We investigated the latter point by the 

 following experiment : 



We had a leaden globe made, capable of containing about two 

 pints, wine measure, and of tolerable thickness, so as to support 

 considerable pressure. We poured water into it through an 

 aperture, which we afterwards closed with melted lead, as soon 

 as the globe was filled with water, so that the whole became 

 perfectly solid. We next flattened the two opposite sides with 

 a heavy hammer, which necessarily caused the water to occupy 

 a less space, since the sphere is the solid of greatest content ; and 

 when hammering failed from the resistance of the water, we 

 made use of a mill or press, till at last the water, refusing to 

 submit to a greater pressure, exuded like a fine dew through the 

 solid lead. We then computed the extent to which the original 

 space had been reduced, and concluded that water admitted such 

 a degree of compression when constrained by great violence. 



