88 SCIENCE IN THE LAST HALF CENTURY. 



cliemical and thermal action, had made extensive progress before 1S37. 

 But the determination of the influence of magnetism on light, the dis- 

 covery of diamagnetism, of the influence of crystalline structure on 

 magnetism, antl the completion of the mathematical theory of electri. 

 city, all belong to the present epoch. To it also appertain the practical 

 execution and the working out of the results of the great international 

 system of observations on terrestrial magnetism, suggested by Hum- 

 boldt in 183Cj and the invention of instruments of infinite delicacy and 

 precision for the quantitative determination of electrical phenomena. 

 The voltaic battery has received vast imi)rovements; while the inven- 

 tion of magneto-electric engines and of improved means of producing 

 ordinary electricity has provided sources of electrical energy vastly 

 suj)erior to any before extant in power, and far more convenient for 

 use. 



It is perhaps this brancli of physical science which may claim the 

 palm for its practical fruits, no less than for the aid which it has fur- 

 nished to the investigation of other parts of the- field of physical sci- 

 ence. The idea of the practicability of establishing a communication 

 between distant points, by means of electricity, could hardly fail to 

 have simmered in the minds of ingenious men, since well-nigh a cen- 

 tury ago, experimental i^roof was given that electric disturbances could 

 be propagated through a wire 12,000 feet long. Various methods of 

 carrying the suggestion into practice had been effected with some de- 

 gree of success; but the system of electric telegraphy, which, at the 

 l)resent time, brings all jDarfcs of the civilized world within a few juin- 

 utes of one another, originated only about the commencement of the 

 epoch under consideration. In its influence on the course of liuman 

 affairs, this invention takes its place beside that of gunpowder, which 

 tended to abolish the physical inequalities of fighting men, — of ])rint- 

 ing, which tended to destroy the effect of inequalities in wealth among 

 learning men, — of steam transport, which has done the like for travel- 

 ling men. All these gifts of science are aids in the process of levelling 

 up; of removing the ignorant and baneful prejudices of nation against 

 nation, province against province, and class against class ; of assuring 

 that social order which is the foundation of progress, which has re- 

 deemed Europe from barbarism, and against which one is glad to think 

 that those who, in our time, are employing themselves in fanning the 

 embers of ancient wrong, in setting class against class, and in trying 

 to tear asunder the existing bonds of unity, are undertaking a futile 

 struggle. The telephone is only second in practical importance to the 

 electric telegraph. Invented, as it were, only the other day, it has 

 already taken its place as an appliance of daily life. Sixty years ago 

 the extraction of metals from their solutions, by the electric current, 

 was simply a highly interesting scientific fact. At the present day 

 the galvano-plastic art is a great industry ; and, in combination with 

 photography, promises to be of endless service in the arts. Electric 



