THE ETHER OF SPACE 293 



speaking, it is not a real strain, but only a "stress" since 

 there can be no actual yield, but only a pull or tension, 

 extending in all directions toward infinity. 



The tension required per unit of matter is almost ludi- 

 crously small, and yet in the aggregate, near such a body 

 as a planet, it becomes enormous. 



The force with which the moon is held in its orbit would 

 be great enough to tear asunder a steel rod four hundred 

 miles thick, with a tenacity of 30 tons per square inch ; so 

 that if the moon and earth were connected by steel instead 

 of by gravity, a forest of pillars would be necessary to 

 whirl the system once a month round their common center 

 of gravity. Such a force necessarily implies enormous 

 tension or pressure in the medium. Maxwell calculates 

 that the gravitational stress near the earth, which we must 

 suppose to exist in the invisible medium, is 3,000 times 

 greater than what the strongest steel could stand ; and near 

 the sun it should be 2,500 times as great as that. 



The question has arisen in my mind whether, if all the 

 visible or sensible universe estimated by Lord .Kelvin 

 as equivalent to about a thousand million suns were all 

 concentrated in one body of specifiable density, 1 the stress 

 would not be so great as to produce a tendency toward 

 ethereal disruption ; which would result in a disintegrating 

 explosion, and a scattering of the particles once more as an 

 enormous nebula and other fragments into the depths of 

 space. For the tension would be a maximum in the interior 

 of such a mass; and, if it rose to the value of 10 33 dynes 

 per square centimeter, something would have to happen. 

 I do not suppose that this can be the reason, but one would 

 think there must be some reason, for the scattered condition 

 of gravitative matter. 



Too little is known, however, about the mechanism of 

 gravitation to enable us to adduce it as the strongest argu- 

 ment in support of the existence of an ether. The oldest 



J On doing the arithmetic, however, I find the necessary concen- 

 tration absurdly great, showing that such a mass is quite insufficient. 



