6o8 THE POPULAR SCIENCE MONTHLY. 



Otto yon Guericke, Burgomaster of Magdeburg, contemporary of 

 Boyle, and inventor of the air-pump, intensified the electric power 

 previously obtained. He devised what may be called the first electrical 

 machine, which was a ball of sulphur, about the size of a child's head. 

 Turned by a handle and rubbed by the dry hand, the sulphur-sphere 

 emitted light in the dark. 



Von Guericke also noticed that a feather, having been first at- 

 tracted toward his sulphur globe, was afterward repelled, and kept 

 at a distance from it, until, having touched another body, it was again 

 attracted. He also heard the hissing of the "electric fire," and ob- 

 served that a body, when brought near his excited sphere, became 

 electrical and capable of being attracted. 



The members of the Academy del Cimento examined various sub- 

 stances electrically. They proved smoke to be attracted, but not 

 flame, which, they found, deprived an electrified body of its power. 



They also proved liquids to be sensible to the electric attraction, 

 showing that when rubbed amber was held over the surface of a 

 liquid, a little eminence was formed, from which the liquid was finally 

 discharged against the amber. 



Sir Isaac Kewton, by rubbing a flat glass, caused light bodies to 

 jump between it and a table. He also noticed the influence of the 

 rubber in electric excitation. His gown, for example, was found to 

 be much more efiective than a napkin. Newton imagined that the 

 excited body emitted an elastic fluid which penetrated glass. 



Dr. \Yall (1V08) experimented with large, elongated pieces of 

 amber. He found wool to be the best rubber of amber. " A prodi- 

 gious number of little cracklings" was produced by the friction, every 

 one of them being accompanied by a flash of light. "This light and 

 crackling," says Dr. Wall, " seem in some degree to represent thunder 

 and lightning." * This is the first published allusion to thunder and 

 lightning in connection with electricity. 



Stephen Gray (1729) also observed the electric brush, snappings, 

 and sparks. He made the prophetic remark, that " though these effects 

 are at present only minute, it is probable that in time there may be 

 found out a way to collect a greater quantity of the electric fire, and, 

 consequently, to increase the force of that power Avhich by several 

 of those experiments, if we are permitted to compare great things 

 with small, seems to be of the same nature with that of thunder and 

 lightning." ' 



Sec. 3. Tlie Art of Experiment. We have thus broken ground 

 with a few historic notes, intended to show the gradual growth of 

 electrical science. Our next step must be to get some knowledge of 

 the facts referred to, and to learn how they may be produced and 

 extended. The art of producing and extending such facts, and of 

 inquiring into them by proper instruments, is the art of experbnent. 



' " Philosophical Transactions," 1708, p. 69. " Ibid., vol. xxxix., p. 24. 



