HISTORY OF SCIENCE. 



both etc. Books published a few years later represent Hawksbee's 

 machine under the simpler form of a single glass globe twwrfbj 

 an axis, as shown in Fig. 158. But for som! timf after devisW the 

 globe apparatus, this experimenter continued to use the still more 

 elementary glass tube held in the hand. 



In 1708 a paper published by Dr. Wall in the "Philosophic Tran- 

 sactions" states, that the author found that amber, sealing-wax ? 

 b^n nd ^ d ' " ^ ^ deCtriCal b dieS ' ^ -nderfd Tummous" 



BLSS^S; J ^ a gCneral Pr perty f dectrical bodies was esta- 

 ilished ; that is to say, it was proved that when a body was by friction 



made to attract light substances, that body at the same time became 



FIG. 154. 



It may be convenient at this stage to point out that we may call 

 electrical all substances which, when rubbed, acquire the property of 

 attracting light bodies. It is usual also to say that bodies are elec- 

 trified, and to call the cause, whatever it may be, of these phenomena 

 electricity (from electron, the Greek name for amber). It may also not 

 be wholly superfluous to remark that these words do not in the slightest 

 degree explain the phenomena in question. They are merely convenient 

 words for expressing certain states of matter and the absolutely un- 

 known cause of those states. The differences observed in the beha- 

 viour of bodies when rubbed caused all substances to be divided into 

 two classes : the one contained all those which could be electrified by 

 friction, to be called electrics or ideo-electrics, such as glass, amber, sealing- 

 wax, etc. ; the other class contained those which showed no signs of 

 electricity when rubbed, such as metals, etc., and these were termed 

 non-electrics or anelectrics. This was a classification established by the 

 next experimenter who appears on the scene that is, STEPHEN GRAY 



