26 JOHN J. STEVENSON 



tions, and just missed discovering the law of gravitation. He 

 laid the foundation for practical application of astronomy to 

 everj^day life. 



In the eighteenth century astronomy was recognized by 

 governments as no longer of merely curious interest, and its 

 students received abundant aid. The improvement of the 

 telescope, the discovery of the law of gravitation, and the 

 invention of logarithms had made possible the notable ad- 

 vances marking the close of the seventeenth century. The in- 

 creasing requirements of accuracy led to exactness in the 

 manufacture of instruments, to calculation and recalculation 

 of tables, to long expeditions for testing methods as well as 

 conclusions, until finally the suggestion of Copernicus, the 

 physician, and of Kepler, the ill fed invalid, became fact, and 

 astronomical results were utilized to the advantage of man- 

 kind. The voyager on the ocean and the agriculturist on land 

 alike reap benefit from the accumulated observ^ations of three 

 centuries, though they know nothing of the principles or of 

 the laborers by whom the principles were discovered. The 

 regulation of chronometers as well as the fixing of boundary 

 lines between great nations is determined by methods due to 

 slow accumulation of facts, slower development in analysis 

 and calculation, and even slower improvement in instruments. 



Galvani's observ^ations that frogs' legs twitch when near 

 a friction machine in operation led him to test the effect of 

 atmospheric electricity upon them. The instant action 

 brought about the discovery that it was due not to atmos- 

 pheric influence, but to a current produced by contact of a 

 copper hook with an iron rail. Volta pursued the investiga- 

 tion and constructed the pile which bears his name. With 

 this, modified, Davy, in 1807, decomposed potash and soda, 

 thereby isolating potassium and sodium. This experiment, 

 repeated successfully by other chemists, was the precursor 

 of many independent investigations, which directed to many 

 lines of research, each increasing in interest as it was followed. 



Volta's croTVTL of cups expanded into the clumsy trough 

 batteries which were displaced finally in 1836 by Daniel's con- 

 stant battery, using two fluids, one of which was cupric sul- 

 phate. De la Rue observed that, as the sulphate was reduced, 



