THE STORY OF NINETEENTH-CENTURY SCIENCE 



the elements came to be known as atomic weights 

 the name Dalton had given them from the first and 

 the tangible conception of the chemical atom as a body 

 of definite constitution and weight gained steadily in 

 favor. 



From the outset the idea had had the utmost tangibil- 

 ity in the mind of Dalton. He had all along represented 

 the different atoms by geometrical symbols as a circle 

 for oxygen, a circle enclosing a dot for hydrogen, and 

 the like and had represented compounds by placing 

 these symbols of the elements in juxtaposition. Berzelius 

 proposed to improve upon this method by substituting 

 for the geometrical symbol the initial of the Latin name 

 of the element represented O for oxygen, H for hy- 

 drogen, and so on a numerical coefficient to follow 

 the letter as an indication of the number of atoms pres- 

 ent in any given compound. This simple system soon 

 gained general acceptance, and with slight modifica- 

 tions it is still universally employed. Every school- 

 boy now is aware that H 2 O is the chemical way of ex- 

 pressing the union of two atoms of hydrogen with one 

 of oxygen to form a molecule of water. But such a 

 formula would have had no meaning for the wisest 

 chemist before the day of Berzelius. 



The universal fame of the great Swedish authority 

 served to give general currency to his symbols and 

 atomic weights, and the new point of view thus devel- 

 oped led presently to two important discoveries which 

 removed the last lingering doubts as to the validity 

 of the atomic theory. In 1819 two French physicists, 

 Dulong and Petit, while experimenting with heat, dis- 

 covered that the specific heats of solids (that is to say, 

 the amount of heat required to raise the temperature of 



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