300 PERSONAL PREPARATION FOR RESEARCH. 



Christian Era, habitually employed the pendulum as a 

 measurer of time in their astronomical observations, neatly 

 600 years before Gralileo discovered the principle of that 

 instrument. Greber, nearly a thousand years before Lavoi- 

 sier made a similar discovery, had stated that if a certain 

 weight of lead, iron or copper, was heated in an open 

 vessel, the metal would weigh more after it was heated 

 than it did before. Cunaeus, in the year 1746, redis- 

 covered the chief property of the Leyden jar, which had 

 been found by Von Kleist during the previous year. Boyle 

 in 1650, and subsequently Mariotte in 1676, found by 

 means of experiments the relation of the density of the 

 atmospheric air to its pressure. The observation made 

 by Nicholas Steno, a Dane, in the year 1669, that although 

 the sides of a hexagonal crystal of quartz might vary, its 

 angles are not changed, appears also to have been redis- 

 covered by Dominic Grulielmim, who says in 1707, 'there 

 is here a principle of crystallization : the inclination of the 

 planes and of the angles is always constant.' Canton in 

 the year 1752, and Wilcke also, discovered that substances 

 in the vicinity of an electrified body acquire an opposite 

 kind of electricity. Dr. Wollaston followed closely upon 

 the heels of Dalton as the original discoverer of the 

 atomic-theory ; in the Philosophical Transactions of the 

 Koyal Society, 1808, he stated that he had observed 

 in various instances the amounts of combined acid in 

 neutral and acid salts to be as 1 to 2 in the two salts, 

 and that it was his intention to ascertain whether or 

 not this was a general law in such compounds, had not 

 Dalton published his more general theory which included 

 this rule. Berzelius also was upon the same track when 

 he heard of Dalton's views ; and he then found that they 

 were fully confirmed by his own numerous analyses. Wol- 

 laston and Fraunhofer discovered the lines in the solar 



