A HISTORY OF SCIENCE 



that amber retained its attractive virtue after the 

 friction that excited it had ceased. " For the attrition 

 having caused an intestine motion in its parts," he 

 says, "the heat thereby excited ought not to cease 

 as soon as ever the rubbing is over, but to continue 

 capable of emitting effluvia for some time after- 

 wards, longer or shorter according to the goodness of 

 the electric and the degree of the commotion made; 

 all which, joined together, may sometimes make the 

 effect considerable; and by this means, on a warm 

 day, I, with a certain body not bigger than a pea, but 

 very vigorously attractive, moved a steel needle, 

 freely poised, about three minutes after I had left 

 off rubbing it." 8 



MARIOTTE AND VON GUERICKE 



Working contemporaneously with Boyle, and a man 

 'whose name is usually associated with his as the pro- 

 pounder of the law of density of gases, was Edme 

 Mariotte (died 1684), a native of Burgundy. Mariotte 

 demonstrated that but for the resistance of the at- 

 mosphere, all bodies, whether light or heavy, dense or 

 thin, would fall with equal rapidity, and he proved 

 this by the well-known " guinea-and-f eather " experi- 

 ment. Having exhausted the air from a long glass 

 tube in which a guinea piece and a feather had been 

 placed, he showed that in the vacuum thus formed 

 they fell with equal rapidity as often as the tube was 

 reversed. From his various experiments as to the 

 pressure of the atmosphere he deduced the law that the 

 density and elasticity of the atmosphere are precisely 

 proportional to the compressing force (the law of Boyle 



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