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SCIENCE. 



[N. S. Vol. XXII. No. 5QM. 



electrical conductivity, that led to this ex- 

 tremely fruitful supposition. 



Conclusion. —li, after this short sum- 

 mary of its properties, we try to look into 

 the nature of matter, we conclude that 

 matter is not continuous, but that there are 

 centers of action which seem to have an 

 eternal existence, changing only in the 

 place that they occupy— these are the 

 atoms. They keep together in some way 

 and form the molecule; how, it is pretty 

 hard to say. The planetary constellation, 

 with ordinary attraction and centrifugal 

 force in equilibrium, is excluded by the 

 consideration that at the absolute zero 

 there is no movement at all. The repulsive 

 force .that we want might be of electrical 

 nature ; and so we come to our combina- 

 tion of material and electrical atoms. 

 There is indeed something fascinating here, 

 and when we admit for carbon that it may 

 unite to four equally charged electrical 

 atoms and hold them by a force of the 

 nature of elasticity, we have at once a pos- 

 sible equilibrium and the tetrahedral 

 grouping. My only difficulty is that an 

 uncharged atom of carbon, coming into con- 

 tact with the ions just described, would 

 take away half the electric charge, and so 

 the valency of any element might be re- 

 duced to unity. The latest supposition, 

 that matter is built up of electricity alone, 

 lies again beyond the scope of this address. 



Let me now turn to the second part of 

 my subject, and touch upon the problem 

 of affinity; indeed, the action that keeps 

 atoms together must be closely related to 

 affinity. 



II. PHYSICAL CHEMISTRY AND OUR NOTIONS 

 CONCERNING AFFINITY. 



While physical chemistry, in the first 

 period of its development, was chiefly de- 

 voted to the study of the physical prop- 

 erties of matter, the second and present 



period is characterized by the predominant 

 place of the problem of affinity. 



This change in the general aspect of 

 our science goes hand in hand with a dif- 

 ferent way of working : in the development 

 of our ideas of matter, physical chemistry 

 introduced physical methods and instru- 

 ments for the study of physical properties ; 

 in the development of our ideas of affinity, 

 physical chemistry has introduced physical 

 principles. 



Affinity Considered as Force. — The first 

 line of thought considered affinity as a 

 force, and in this direction it was natural 

 to think of the Newtonian attraction as the 

 chemical agent. So it was that Berthollet, 

 and with far more success Gulclberg and 

 AVaage, applied the laws of mass action to 

 problems of affinity, formulating a rela- 

 tion still known as the mass law, according 

 to which affinity is proportional to the 

 weight in the unit of volume. 



Now, as we all know, affinity is of a 

 specific nature, and does not depend on 

 weight merely; on the contrary, the least 

 heavy elements are generally the most act- 

 ive. So Berzelius built up his system 

 founded on the notion that elements have 

 a specific electrical character, either posi- 

 tive or negative, and, in combining, act by 

 electrical attraction. In this direction 

 Helmholtz made a further step in taking 

 into account the quantitative side. Con- 

 sidering the electrical charges involved in 

 Faraday's law, he pointed out as very im- 

 - portant that the attraction due, for in- 

 stance, to the negative charge in chlorine 

 and the positive one in hydrogen far ex- 

 ceeds the gravitational attraction of the 

 masses. Yet a satisfying notion of affinity 

 was not obtained in this way. 



Affinity Measured as Work. — A second 

 line of thought took into consideration not 

 the force but the work that affinity repre- 

 sents; and it seemed a decisive step when 

 Thomsen and Berthelot declared that the 



