362 



SCIENTIFIC THOUGHT. 



of mass, which in the Newtonian formula meant merely 

 the quantity of matter, had indeed to be enlarged, and 

 to the attracting forces had to be added those of re- 

 pulsion ; still, though physically the phenomena were 

 entirely different, the mathematical expression which 

 ruled the two electric and the two magnetic quantities, 

 usually termed fluids, looked very much like the New- 

 tonian gravitation formula : it betrayed philosophers into 

 thinking they possessed an explanation where really they 

 had only a measurement and a description.^ 



Newton's elementary law of gravita- 

 tion, Laplace as it were summing 

 up the evidence in his great work. 

 What Laplace did for Newton was 

 done by Poisson for Coulomb's ele- 

 mentary law of electric and mag- 

 netic action, and on a still larger 

 scale by Gauss, who worked out 

 the mathematical theory and ap- 

 plied it to the case of the magnetic 

 distribution on the earth's sur- 

 face. In England, already before 

 Coulomb's researches were pub- 

 lished, Cavendish had, likewise by 

 a combination of experiment and 

 calculation, established the elemen- 

 tary formulte and properties of 

 electrical phenomena. See note to 

 the following page. 



^ The exact measurements of 

 Coulomb and the mathematical 

 analysis of Poisson and Gauss 

 superseded the vaguer discussions 

 on the nature of electricity and 

 magnetism which were very fre- 

 quent before that period, just as 

 the mathematical principles of 

 Newton and Laplace drove into 

 the background the discussion on 

 the nature and cause of gravity. 

 Coulomb himself does not profess 

 to settle the controversy carried on 

 between the two schools of which 

 Dufay and Franklin can be con- 

 sidered as the principal representa- 



tives viz., whether there existed 

 two electric fluids or only one. 

 Coulomb judged the rival views 

 simply as to their usefulness in 

 describing and measuring phenom- 

 ena : " Comme ces deux e;s:plications 

 n'ont qu'un degr^ de probabilite 

 plus ou moins grand je previens, 

 pour mettre la theorie ... a 

 I'abri de toute dispute systematique, 

 que dans la supposition des deux 

 fiuides electriques je n'ai d'autre 

 intention que de presenter avec le 

 moins d'elcments possibles, les re- 

 sultats du calcul et de I'experience, 

 et non d'indiquer les veritables 

 causes de I'electricitc^ " (' Collection 

 de Memoires,' vol. i. p. 252). He 

 had previously, in 1777, rejected 

 the theory of vortices to explain 

 magnetic phenomena: "II semble 

 qu'il resulte de I'experience que ce 

 ne sont point des tourbillons qui 

 produisent les difFerents phenom- 

 enes aimantains, et que, pour les 

 expliquer, il faut necessairement 

 recourir a des forces attractives et 

 repulsives de la nature de celles, 

 dont on est oblige de se servir pour 

 expliquer la pesanteur des corps et 

 la physique cdleste " (vol. i. p. 8). 

 And in 1789 he is still more 

 cautious : " Pour dviter toute dis- 

 cussion, j'avertis . . . que toute 

 hypothese d'attraction et de rdpul- 



