THE ATOMS OF THE ELEMENTS. 19 



Our present question is: Are they related to one an- 

 other ? Now, if there be any relation among these atoms, 

 it should show in their weights. The first thing, there- 

 fore, we shall notice is the number attached to each in the 

 table above. This number stands for the atomic weight; 

 in other words, for the number, of times heavier that 

 particular atom is than the hydrogen atom which is the 

 lightest and the unit. These numbers afford an example 

 of the highest accuracy of hand and brain that science 

 has to show. It is true that if you look at the number 

 attached to hydrogen you will find it placed at 1.008 in- 

 stead of 1, as you would suppose, but that is for a certain 

 reason that will soon be made clear. 



PROUT'S HYPOTHESIS. 



In the early days when men first began to determine the 

 relative weights of the atoms, it was noticed that the atomic 

 weights of quite a number of the elements, taking hydrogen 

 as unity, were either whole numbers or very nearly whole 

 numbers, and in 1815 Prout suggested that this numerical 

 regularity could be explained on the assumption that the 

 atoms of the different elements were simply condensations 

 of the hydrogen atom; for obviously if, for example, the 

 weight of the oxygen atom were 16 and that of the carbon 

 atom were exactly 12 times as heavy as the hydrogen atom, 

 then these little bodies could be explained by assuming that 

 they were built up of 16 and 12 hydrogen atoms respec- 

 tively, and there would be an end of the mystery. This 

 idea was at first very kindly received, but as men became 

 more and more accurate in their work, it was soon discov- 

 ered that Prout's method of calmly dropping the decimals 

 after the whole numbers as due to experimental errors would 

 not do, nor would anything like it do. 



It became evident that though many of the atomic 



