ATTEMPTS TO EXPLAIN GRAVITATION 259 



Outside the plates we have opposite effects in the same direction, hence 

 they annul. Between the plates we have opposite effects in opposite 

 directions and the effects are equivalent and hence cumulative. The 

 tension will depend upon the number of lines and the closeness to- 

 gether. Each positive line will increase the tension of a positive line 

 and a negative line will diminish the tension of a positive line. If a 

 positive line increases the tension of a positive line just as much as a 

 negative line decreases it, and if a negative increases the tension of a 

 negative just as much as a positive decreases it, then the resultant ten- 

 sion between the plates will be zero, since there are just as many positive 

 as negative lines. But if the effect (increase) of a positive on a posi- 

 tive is not the same as a negative on a positive there will be a resultant 

 tension between the plates. 



Now take an unelectrified body which we consider an assemblage of 

 positive and negative charges. Lines of force will start on the positive 

 charges and terminate on the negative ones, and just as there was a 

 tension between the plates if the effect of a positive on a positive was 

 not the same as a negative on a negative, so there will be a tension 

 around this unelectrified body, if the above is true. Hence by making 

 the assumption that the lines of force from a positive charge are not 

 the same as those from a negative charge, the increase in tension of a 

 positive on a positive is not the same as the decrease of a negative on a 

 positive and we shall have a resulting tension. This might give rise ta 

 forces in the body of which the most important is gravitation. Here 

 are Professor Thomson's own words taken from my class notes : " Matter 

 I regard as made up of positive and negative charges. . . . Each unit 

 charge is the termination of a line of force. I do not regard the posi- 

 tive and negative lines side by side as the same." 



If you are looking for a Herculean task put the theory to test. 

 Before starting let me remind you that the effect of the earth's field 

 on an electron is something like 30 million times that of gravity and 

 that it is not easy to screen a magnetic force. We see then that this 

 theory is beset with difficulties before which the experimenter at present 

 is helpless. Again, it complicates the simplicity of the electronic theory 

 of electricity. Again, electrical attraction depends upon the medium. 

 On this theory should not gravitational attraction also depend upon the 

 medium? A summary of Professor Thomson's lectures on gravitation 

 was published in Cambridge Philosophical Society Proceedings during 

 the spring of 1909. 



Various other theories have been promulgated but they must be 

 passed by. Those interested in the subject will want to read Osborne 

 Reynold's theory. Kelvin's hydrodynamical theory, which involves both 

 the creation and destruction of matter, is rather unique. 



Some despairing of ever finding a physical explanation have taken 



