658 Mr. W. Sutherland on the Electric 



directed repel one another with a force equal to their attrac- 

 tion when similarly directed. According to the prevailing 

 conceptions of the kinetic theory of gases, it seemed at that 

 time necessary to assume that any two molecules in a gas 

 would have their polar axes, if they possessed such, oppositely 

 directed for as long a time as similarly directed, that there- 

 fore they would repel one another as much as they could 

 attract, and that polar forces would not account for cohesion 

 such as had been proved to exist in gases. Ignoring this 

 difficulty, Fessenden in America proposed to trace cohesion 

 to the attraction of opposite electrical charges for one another 

 (see Phys. Review, x. 1900, with references to El. World, 

 1891, and Science, 1892, 1893). He seems to have obtained 

 most encouraging results, even afc these early dates, from 

 statical considerations alone, neglecting the kinetics of mole- 

 cules. This ignoring of kinetics and of the repulsion between 

 like charges of electricity was the probable cause of the 

 failure of Fessenden's ideas to secure the attention of 

 physicists. They remained almost unknown. Peinganum 

 (Pliys. Zeitschr. 1900 ; Ann. der Phys. [4] x. 1903) treated 

 cohesion as of electrostatic origin, considering each molecule 

 to have a pair of electrons at a certain distance apart. This 

 of course gave him attractions and repulsions according to 

 the law of the inverse fourth power. He eliminated repul- 

 sions by the consideration that by their mutual directive 

 influence two neighbour molecules would cause one another's 

 electric axes to be similarly directed along the line joining 

 their centres. This is one step towards accounting for mole- 

 cular attraction by means of electric bipoles, but it needs 

 extension to show how the cohesive forces in gases are to be 

 explained satisfactorily. 



As regards gases, the main difficulty is still for the most 

 part ignored. In solids another difficulty is possible, namely, 

 that the distance between the centres of two neighbour 

 molecules may be nearly equal to the distance between the 

 two opposite electrons of a molecule. In this case the law 

 of the inverse fourth power breaks down, and must be 

 replaced by the more complex law for two large magnets 

 almost in contact. This difficulty will be considered imme- 

 diately. In " The Electric Origin of Molecular Attraction " 

 (Phil Mag. [6] iv. 1902, p. 625) I sought to show that the 

 cumulative effect of the evidence in my papers on molecular 

 attraction between 1886 and 1902 pointed to electrical 

 polarity as the cause of molecular attraction. To avoid the 

 difficulty of the repulsion between molecules having their 

 electric axes oppositely directed, especially in the case of 

 gases, I introduced the consideration that a pair of attracting 



