686 LECTURE LX. 



and Franklin. As early as 1735 it was remarked by Gray, that "the 

 electric fire seemed to be of the same nature as lightning,"* and their 

 identity was afterwards more strongly asserted by Winkler, and experi- 

 mentally demonstrated by Franklin. The shock of a charged jar was first 

 discovered by Kleist, in 1745 ; and the experiment was repeated by Lalla- 

 mand and Musschenbroek, who described its disagreeable effects on the 

 sensations with an exaggeration not the most philosophical. The theory of 

 the nature of the charge was the second great improvement made by 

 Dr. Franklin in this science. 



The introduction of the Linnean system of botany and zoology is to be 

 considered as bringing near to perfection the logic and phraseology of 

 natural history ; nor has its celebrated author wholly neglected the philo- 

 sophy of the science. The number and the diligence of his successors have 

 already furnished to the different departments of natural history a much 

 ampler store of observations than could easily have been expected from the 

 short time which their labours have occupied. Buffon had merit of a dif- 

 ferent kind, and though his fancy was too little regulated by mathematical 

 accuracy, the elegance of his writings have made their subjects highly 

 interesting to the general reader. Among other modern naturalists of 

 great respectability, Spallanzani, Daubenton, Degeer, Geoffrey, Pennant, 

 the Jussieus, Lacepede and Haiiy, have particularly distinguished them- 

 selves by the importance of their discoveries, and the accuracy of their 

 descriptions. 



. The absorption of heat, during the conversion of ice into water, appears 

 to have been separately observed by Deluc, Black, and Wilke, about the 

 year 1755. On this experiment Dr. Black principally founded his doc- 

 trine of latent heat, supposed to be retained in chemical combination by the 

 particles of fluids. Dr. Irvine and Dr. Crawford explained the circum- 

 stances somewhat differently, by the theory of a change of capacity for 

 heat only. Bergmann,t Lavoisier, Laplace, Kirwan, Seguin, and many 

 other philosophers have illustrated, by experiments and calculations, the 

 various opinions which have been entertained on this subject ; and few 

 chemists, from the times of Boerhaave, Stahl, and Scheele to those of 

 Priestley and other later authors, have left the properties of heat wholly 

 unnoticed. 



The elegant hypothesis of Aepinus, respecting magnetism and electricity, 

 founded in great measure on the theory of Franklin, was advanced in 1759 ; 

 our venerable countryman, Mr. Cavendish, had invented a similar theory, 

 and had entered in many respects more minutely into the detail of its con- 

 sequences, without being acquainted with Aepinus's work ; although the 

 publication of his paper on the subject was 12 years later. Lambert, 

 Mayer, Coulomb, and Robison have also pursued inquiries of a similar 

 nature, both theoretically and experimentally, with great success. The 

 electrophorus of Wilke, and the condenser of Volta, are among the earliest 

 fruits of the cultivation of a rational system of electricity, and Mr. 

 Cavendish's investigation of the properties of the torpedo may 'serve as 



* Ph. Tr. xxxix. 24. 



t Opuscula Physica et Chemica, 6 vols. Upsalise. 



