40 



SCIENCE 



[N. S. Vol. XLIV. No. 1124 



not acted upon by some new force. The 

 idea of inertia, conceived by Galileo and 

 amplified by Newton, was one of the start- 

 ing points of both modern philosophy and 

 modern physics. So far as we know, weight 

 and inertia run parallel to each other. Of 

 any two adjacent bodies, that having 

 greater weight has also greater inertia. 

 Hence they may be determined at one and 

 the same time, and this Siainese-twinlike 

 conjunction of properties establishes itself 

 at once as perhaps the most fundamental of 

 all the attributes of matter. Next perhaps 

 comes volume, the attribute which enables 

 matter to occupy space, with the corollaries 

 dealing with the changes of volume caused 

 by changes of temperature and pressure. 

 Other fundamental properties are the 

 tendency to cohere (which has to do with 

 the freezing and boiling points of the 

 liquids) and the mutual tendency of the 

 elements to combine, almost infinite in its 

 diversity, which may be measured by the 

 energy-changes manifesting themselves dur- 

 ing the reaction of one substance with an- 

 other. 



These are only a few of the important 

 properties of the elements, but they present 

 an endless prospect of further investigation, 

 in spite of all that has been done during the 

 past hundred years. For as yet we know 

 only the surface of these things, and com- 

 prehend but little as to the underlying con- 

 nections between them and the reasons for 

 their several magnitudes. "Why, for ex- 

 ample, should oxygen be a gas, having an 

 atomic weight just four times as great as 

 that of helium, and why should it have an 

 intense affinity for sodium and no affinity 

 whatever for argon or fluorine? No man 

 can answer these questions ; he can discover 

 the facts, but can not yet account for them. 

 The reasons are as obscure and elusive as 

 the mechanism of gravitation. But we shall 

 not really understand the material basis 



upon which our life is built until we have 

 found answers to questions of this sort. 



In order to correlate the properties of the 

 elements, and to attain any comprehension 

 of their significance, one must first exactly 

 ascertain the facts. Therefore, my endeavor 

 has been to institute systematic series of 

 experiments to fill the gaps in our knowl- 

 edge of the actual phenomena. In much of 

 this work I have had the invaluable aid of 

 efficient collaborators, for which I am 

 grateful. 



The atomic weights were the first of the 

 fundamental properties of the elements to 

 receive attention in carrying out this plan. 

 These, as every one who has studied ele- 

 mentary chemistry knows, represent the 

 relative weights in which substances com- 

 bine with one another. They are called 

 atomic weights rather, than merely combin- 

 ing proportions because they can be ex- 

 plained satisfactorily only by the assump- 

 tion of definite particles which remain indi- 

 visible during chemical change. Even if 

 some of these particles or so-called "atoms" 

 suffer disintegration in the mysterious proc- 

 esses of radioactive transformation, the 

 atomic theory remains the best interpreta- 

 tion of the weight-relations of all ordinary 

 chemical reaction. Indeed, it is entrenched 

 to-day as never before in man's history. 



The determination of atomic weights is, 

 primarily, a question of analytical chemis- 

 try — a question of weighing the amount of 

 one substance combined with another in a 

 definite compound — but its successful prose- 

 cution involves a much wider field. First, 

 the substances must be prepared and 

 weighed in the pure state, and next, they 

 must be subjected to suitable reactions and 

 again weighed with proof that in the proc- 

 ess nothing has been lost and nothing acci- 

 dentally garnered into the material to be 

 placed on the scale pan. These require- 

 ments involve many of the principles of the 



