;8 AN INTRODUCTION TO SCIENCE 



size, and therefore in all its properties, from the atoms of 

 every other element. If it were possible for us to see the 

 atoms, we could with a certain scale of relative sizes (atomic 

 weights) say which atoms were those of phosphorus, which 

 of silver, and so on. 



Before, therefore, he studies the architecture of matter, 

 the chemist examines the constructive materials which 

 Nature uses. He finds that she builds with some seventy 

 different elements. As we have already said, he recognises 

 each of these various, elements by the size of the atoms of 

 which it is composed. 



It has long been suspected that the chemical unit or atom 

 is not, as its name implies, "an ideally indivisible portion of 

 matter." On the contrary, it would seem that the true atom 

 cannot under any conditions be made to act as a unit. 

 Nature has arranged the true atoms into groups, which 

 always act as groups, and each of which is therefore, for all 

 practical purposes, an atom. We cannot break up the 

 groups, and we can conceive them as divisible only in a 

 universe quite different to the universe that we know. 



According to this modern conception of the nature of 

 matter, there is but one fundamental substance, protyle. 

 This arch-element does not exist except in various states of 

 condensation or groupings of atoms held together by indis- 

 soluble bonds. The "atoms " of all the elements, even the 

 lightest of them, hydrogen, are aggregations of protyle- 

 atoms. 



We owe this conception of an arch-element in various 

 fixed degrees of condensation to Mendeleef's discovery 

 that all the elements with which we are acquainted can be 

 arranged in series according to the numerical value of their 

 atomic weights. The chemist cannot estimate the weight 

 of an atom, but he can determine the. amount of any given 

 element, which enters into combination with other elements, 

 relatively to the amounts of the elements with which it 

 combines. Dalton (1802) pointed out that if all possible 



