ON THE HISTORY OF TERRESTRIAL PHYSICS. 587 



a model of accuracy and precision in the conduct of experimental 

 researches. 



The speculations of Boscovich respecting the fundamental properties of 

 matter, and the general laws of the mutual action of bodies on each other, 

 have been considered by some candid judges as deserving the highest com- 

 mendation ; they remain however almost in all cases speculations only ; 

 and some of the most intricate of them, being calculated for the explanation 

 of some facts, which have perhaps been much misunderstood, must con- 

 sequently be both inaccurate and superfluous. 



The attention of several experienced philosophers, who are now living, 

 has been devoted, with much perseverance, to the difficult subject of 

 hygrometry. Deluc's experiments have offered us a very useful compari- 

 son of the hygrometrical qualities of various substances : Saussure has 

 investigated, with great labour, the indications of the hygrometer and the 

 thermometer, as connected with the presence of a certain portion of vapour, 

 contained in air of various densities; and Pictet has ascertained some 

 similar circumstances respecting vapours of different kinds wholly un- 

 mixed with any air. The hypotheses, which have usually accompanied 

 the relation of most of these experiments, have however been in general 

 too little supported by facts to be entitled to universal adoption. 



For some years past, the philosophical, as well as the unphilosophical 

 world has been much occupied and entertained by the discoveries of Gal- 

 vani, Volta, and others, respecting the operations of the electric fluid. The 

 first circumstance that attracted Galvani's attention to the subject of 

 animal electricity, was the agitation of a frog, that had a nerve armed, 

 that is, laid bare and covered with a metal, when a spark was taken in 

 its neighbourhood. A person acquainted with the well known laws of 

 induced electricity might easily have foreseen this effect : it proved, how- 

 ever, that a frog so prepared was a very delicate electrometer, and it led 

 Galvani to further experiments. It has been shown by Volta, that an 

 entire frog may be convulsed by a degree of electricity which affects 

 an electrometer but very weakly ; but that when prepared in Galvani's 

 manner, it will be agitated by an electricity one fiftieth part as great, 

 which cannot be discovered, by any other means, without the assistance 

 of a condenser. Galvani, however, found that a communication made 

 between the armed nerve and its muscle, by means of any conducting 

 substance, was sufficient to produce a convulsion, without the presence of 

 foreign electricity : hence he concluded that the nerve and muscle, like 

 the opposite surfaces of a charged jar, were in contrary states of electri- 

 city, and that the communication produced a discharge between them. 

 He observed, however, a considerable difference in the effects, when dif- 

 ferent metals were employed for forming the circuit ; and this circum- 

 stance led to the discovery of the excitation of electricity by means of a 

 combination of different inanimate substances only, which Mr. Davy 

 attributes to Fabroni, Creve, and Dr. Ash. It was, however, still more 

 satisfactorily demonstrated by Volta ; and he at first supposed that all 

 the phenomena observed by Galvani were derived from effects of this 

 kind, but on further examination he was obliged to allow the independent 



