362 ACROPHTSICS. 



which was sanctioned by Boyle and Newton. The other doctrine, 

 that heat is produced by a peculiar subtile fluid, was maintained by 

 Boerhaave, and is, we believe, the one more generally adopted, in 

 explaining the phenomena. The first invention of the Thermometer, 

 is by some writers ascribed to Drebbel of Holland ; but more gene- 

 rally to Sanctorio of Italy, about the year 1626. The temperature 

 was at first measured by the expansion of air ; and afterwards by 

 that of alcohol ; till in 1720, Fahrenheit, of Dantzic, proposed the 

 use of mercury, and introduced the graduation which bears his name. 

 Wedge wood's Pyrometer was invented in 1731 : and the use of 

 concave mirrors for reflecting heat, appears to have been discovered 

 by Lambert of Germany, in 1758. The discovery of latent heat, 

 was made by Dr. Black of Edinburgh, in 1757 ; and radiant heat 

 was first identified by Scheele, about 1770. We have only room to 

 add that the invention of the galvanic battery, by Cruikshank, and 

 of the compound blowpipe, by Dr. Hare, have furnished the most 

 powerful means of producing heat yet discovered. 



The knowledge of Electricity, possessed by the ancients, was 

 simply the fact, known to Thales, that amber, when rubbed, acquired 

 the power of attracting light bodies. In the year 1600, Dr. Gilbert 

 announced his discovery of several other electrics ; and first suggested 

 the idea of an electric fluid, or effluvium. Otho Guericke, about 1 650, 

 constructed the first electric machine, by mounting a globe of sulphur; 

 with which he produced electric light, and sound. In 1733, Dufaye 

 discovered that two electrics, when rubbed together, become oppo- 

 sitely excited ; on which fact he founded his theory of two fluids ; 

 the one collecting on glass, which he called vitreous ; the other on 

 sealing wax, or rosin, hence called resinous electricity. Dr. Franklin 

 proposed the theory of one fluid, which, when accumulated, consti- 

 tutes the vitreous or positive state ; but when abstracted or deficient, 

 causes the resinous or negative state, or excitement. In 1746, the 

 Leyden jar was discovered by Cuneus and Muschenbroek ; and in 

 1752, Dr. Franklin made his great discovery that the electric fluid is 

 the cause of lightning. The later electric discoveries, belong chiefly 

 to Galvanism ; under which they will be mentioned, in connection 

 with their theoretical relations. Those of Professor Faraday, and of 

 our countryman, Professor Henry, concerning electric induction and 

 electro-motion, are brilliant, but transcend our present limits. 



The attraction of the Magnet, or loadstone, for iron filings, was 

 known to Thales ; but its property of pointing to the poles of the 

 earth, though said to have been known to the Chinese, 1120 B. C., 

 appears to have been first known in Europe, to the French ; who 

 availed themselves of it, in Navigation, about A. D. 1150: and the 

 Mariner's compass was improved, rather than invented, by Flavio 

 Gioia, in 1302. The variation of the compass, was first noticed by 

 Columbus, in 1492: and the dip, was first made known by Robert 

 Norman, in 1581. Dr. Gilbert explained the polarity of the needle 

 by considering the earth as a large magnet attracting it; and .ZEpinus 

 proposed a magnetic theory similar to the electric theory of Dr. 

 Franklin. Dr. Knight invented the mode of magnetizing by single 

 touch, in 1745 ; and Mr. Mitchell's mode, bv double touch, was made 



