254 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1933 



These are exactly right for studying transient effects like those of 

 lightning, but the impulse generator is inherently incapable of serv- 

 ing' properly any purpose which requires a steady and reasonably 

 constant source of high voltage. The discharge in this impulse gen- 

 erator lasts only a few hundred thousandths or millionths of a 

 second. 



This impulse generator represents the peak of high-voltage accom- 

 plishment by the electromagnetic method, and you will notice that 

 this is accomplished by combining with the electromagnetic device, 

 namely, the step-up transformer, a series of condensers which are 

 essentially electrostatic instruments. 



Let us return now from the high-voltage developments, based 

 on principles of electromagnetism, to the historically earlier type 

 of electric generation which falls within the general field known as 

 electrostatics.^ The characteristic of these devices has been the rela- 

 tive ease of producing high voltages, but with an exceedingly 

 minute quantity of electricity. 



The first electrical machines of which we have any knowledge 

 were frictional electrical machines constructed about 1663 by Otto 

 von Guericke. They consisted of globes of sulphur made to rotate 

 about an axis so as to rub against the hands if held against them. 

 In this way the globe of sulphur became electrically charged, and 

 the charge of the opposite sign appeared on the person who touched 

 the globe. Isaac Newton appears to have been the first person to 

 use a glass globe instead of sulphur, but it was Ramsden in 1768 

 who really constructed the first object that might really be called 

 an electrical generating machine. 



The Ramsden machine consists of a glass plate which can be 

 rotated by a winch and which passes with rubbing contact between 

 two leather pads. By friction the glass becomes positively charged 

 and the pads are negatively charged. These positive charges are 

 taken off the glass disk as it passes in rotation between combs of 

 sharp points. Similarly the negative electricity from the pads is 

 collected from them and delivered to another terminal. For a num- 

 ber of years the only development of the art of electrical generation 

 consisted in finding various materials which might be put on the 

 glass or on the leather pads to increase their effectiveness in separat- 

 ing frictional electricity. 



A later development of a frictional machine is that invented by 

 Lord Armstrong of Newcastle, England, in 1841. Lord Armstrong 

 was experimenting with steam boilers. By accident one of his assist- 

 ants received an electric shock when he touched a piece of metal 

 against which a jet of steam from a leaky boiler was striking. This 

 led Lord Armstrong to further experiments leading to the steam 



