OTTO GUERICKE 59 



differences given by the sense of smell, these air-bubbles, as 

 well as the whole atmosphere of the earth, appeared as 

 resulting from the escape of volatile constituents from solid 

 substances. Guericke also states quite correctly, that on 

 account of the volatility of all bodies, empty space can always 

 be obtained only approximately, but that this does not 

 prevent our drawing conclusions with respect to it. 



The fact that the atmosphere exerts the great pressure now 

 rendered so obvious, Guericke ascribed entirely to its weight; 

 the 'horror of a vacuum' was abolished completely. Instead, 

 he determined directly the specific gravity of air, which 

 Galileo estimated indirectly, by comparing the weight of 

 the same vessel empty and when filled with air, whereby a 

 particularly convincing proof of the considerable weight of 

 quite moderate amounts of air was given by the visible 

 increase in weight of an evacuated vessel while upon the 

 balance, when air was allowed to stream in. Guericke also 

 recognised that we cannot ascribe a definite specific gravity 

 to air, but that it varies with both pressure and temperature. 

 The earth's atmosphere is thus held together by its own 

 weight, and on the surface of the earth it is pressed together 

 to its own density. The vast space between the heavenly 

 bodies Guericke already recognised as empty of all matter. 



Through Guericke's investigations, the air became for us 

 for the first time an object which could be grasped; a body 

 which, like solid and liquid bodies, could be introduced into 

 and removed from a space at will. It also became possible 

 to determine by direct observation how space filled with air 

 differs from empty space. Guericke made use of this in 

 two particularly important matters; he first considered the 

 propagation of light and sound in empty space. He points 

 out that empty space, contrary to the opinion at that time, 

 does not prevent light passing through it, since objects con- 

 tained in it are seen. But his experiments with sound gave a 

 different result. A clockwork which continually struck a bell 



