204 THE POPULAR SCIENCE MONTHLY. 



tioned to the square of the distance to be traveled. Therefore, the 

 velocity has no constant fixed value, but varies with the length of the 

 journey. This law, which is deduced from the mathematical theory of 

 Ohm, introduces order among the experiments, where, otherwise, there 

 would be chaos. It is not surprising that Wheatstone and the readers 

 whom he addressed were misled by the original facts. Few men who 

 have rendered signal services to science, and who have finally reached 

 the highest pinnacle of fame, have suffered more from poverty and 

 neglect, and waited longer for a recognition of their merits, than the 

 modest student of Nuremberg. The slender volume which will per- 

 petuate his name was indeed published at Berlin in 1827, and ante- 

 dates Wheatstone's experiments by seven years. But the book was 

 treated with contempt by a minister of state, to whom Ohm presented 

 a copy, at his University of Cologne, and was first brought to the 

 notice of English readers in 1841, when an English translation of it 

 was effected through the agency of the British Association, and the 

 Copley medal was presented to Ohm by the Royal Society of London. 

 As late as 18G0, when the same work was rendered into French, the 

 translator admits that the mathematical theory of Ohm on the galvanic 

 circuit, the elements of which have since rapidly circulated iu popular 

 text-books, was almost unknown in France, that high seat of science. 

 If the serene but steady light of mathematics had not been dimmed 

 by the blaze of experimental successes, and the teachings of Ohm had 

 been heeded sooner, the science of electricity would have been the 

 gainer, and the men of science would have been saved the mortifica- 

 tion of treating the electro-magnetic telegraph as an impracticability. 

 When Wheatstone was a candidate to fill a vacancy in the cor- 

 responding members of the French Institute, it was objected that he 

 had only made a brilliant experiment, but had not discovered a new 

 principle. Arago came to his rescue, and asserted that he had intro- 

 duced a powerful and fertile method of experimentation which would 

 be felt in other sciences besides electricity. The French physicist lost 

 no time in devising means for making good these claims. If it could 

 be proved experimentally that the velocity of light was greater in air 

 than in water, a capital fact in the contending theories of light would 

 be settled forever. Arago planned the experiment and pressed its 

 feasibility upon the Academy of Sciences with all the power and elo- 

 quence of his nature. At last he roused two younger physicists to 

 undertake what his growing infirmities prevented him from doing 

 with his own hands. The result declared in favor of undulations, and 

 a fatal blow was dealt to the corjmscular theory of light which had 

 vexed science since the days of Newton. If Fizeau and Foucault 

 drew their inspiration from Arago, they owed their success to nothing 

 except their own skill in devising and executing. Having tried the 

 temper of their steel on this easier problem, they were ready for the 

 grand attack, which was, to measure the absolute velocity of light. 



