470 Mr. A. P. Chattock on an 



unstrained condition ; assuming that the cohesion does not 

 increase on the application of stress, which seems unlikely. 

 Now the tenacity of quartz in fibres of ordinary thickness is 

 about 7 x 10 9 *. Hence the internal pressure must be at 

 least equal to this ; and as its calculated value is so much 

 less, its true value will probably not greatly exceed 7 x 10 9 (as 

 it might have done if its calculated value had been larger). 



For the purpose, therefore, of obtaining the order of mag- 

 nitude of q from the above equation (which is all that can be 

 hoped for from such a rough calculation), it will probably be 

 allowable to write tenacity for internal pressure in the formula, 

 bearing in mind, however, that the value of q so obtained will 

 be too small. Putting for d the value ^ x 10~ 8 cm., we have 



<S> 7xl ° 9 ' 



whence 2 >5xl0-^ 



a number which is not to be distinguished from the ionic 

 charge of hydrogen. Of course the extreme closeness of the 

 agreement is purely accidental ; but I cannot think that the 

 agreement of the values of q calculated by the above three 

 independent methods, both with each other and with the ionic 

 charge, can be due to mere chance. 



On the other hand, it does not follow immediately that 

 cohesion is due to electrical attraction because a good value 

 can be calculated from ionic charges. As Dr. Lodge has 

 shown f, the work done by the attraction of two oppositely 

 charged ions is of the same order of magnitude as that done 

 by their chemical affinity in bringing them together ; and 

 consequently, if cohesion can be shown to be numerically 

 equal to either of these forces, it may just as well depend on 

 one as on the other. It is only when considered in con- 

 nexion with the electrical properties of crystals (for which, if 

 the view here put forward be accepted, initially charged 

 molecules are required on electrical grounds) that the above 

 result suggests that cohesion may turn out to be an electrical 

 and not a chemical phenomenon. The idea is at any rate in 

 accordance with the most striking feature of cohesive attrac- 

 tion — its variation, namely, in inverse proportion to a high 

 power of the distance between the cohering particles. For a 

 mass of oppositely charged particles this power could not be 

 less than the cube, and would probably be nearer the fourth 

 power. 



* Boys, 'Nature,' xl. p. 249. His value is 7'8xl0 9 = 50 tons to the 

 inch. 



f " Seat of E.M.F." 



