THE SUCCESSORS OF GALILEO 



many things regarding the action of gases, among 

 others, that animals cannot live in a vacuum. He in- 

 Dented the anemoscope and the air-balance, and being 

 enabled to weight the air and note the changes 

 that preceded storms and calms, he was able still 

 further to dumfound his wondering fellow - Magde - 

 burgers by more or less accurate predictions about the 

 reather. 



Von Guericke did not accept Gilbert's theory that 

 :he earth was a great magnet, but in his experiments 

 along lines similar to those pursued by Gilbert, he not 

 only invented the first electrical machine, but discov- 

 ered electrical attraction and repulsion. The electrical 

 machine which he invented consisted of a sphere of 

 sulphur mounted on an iron axis to imitate the rotation 

 of the earth, and which, when rubbed, manifested elec- 

 trical reactions. When this globe was revolved and 

 stroked with the dry hand it was found that it attached 

 to it "all sorts of little fragments, like leaves of gold, 

 silver, paper, etc . " " Thus this globe, ' ' he says, * ' when 

 brought rather near drops of water causes them to 

 swell and puff up. It likewise attracts air, smoke, 

 etc." 9 Before the time of Guericke's demonstrations, 

 Cabaeus had noted that chaff leaped back from an 

 " electric," but he did not interpret the phenomenon as 

 electrical repulsion. Von Guericke, however, recog- 

 nized it as such, and refers to it as what he calls "ex- 

 pulsive virtue." "Even expulsive virtue is seen in 

 this globe," he says, "for it not only. attracts, but also 

 repels again from itself little bodies of this sort, nor 

 does it receive them until they have touched some- 

 thing else." It will be observed from this that he was 



VOL. II. 15 213 



