KINETIC THEORIES OF GRAVITATION. 227 



The force of the objection contained in onr fourth condition-precedent 

 is thus courageously confronted and defied : " It might be conceived 

 that the attraction would be less on a body moving toward the central 

 body, and greater on one moving from it, which is contrary to what we 

 find by experience. Though regarded mathematically, such an infer- 

 ence would be strictly true, yet since the difference between the forces 

 will depend on the activity of the medium, and since this activity will 

 be increased in proportion to the tenuity of the parts of the medium, it 

 is evident that the setherial atoms may be so small, and the activity of 

 the medium consequently so great, that the swiftest motions we know 

 of could produce no sensible difference in the vigor of its action. , ' And 

 with a marvelous boldness of assumption he adds : " We may hence 

 fairly conclude that there might be a fluid medium pervading the 

 heavens, and all bodies, of such activity that no sensible difference 

 could be observed in the intensity of its action on bodies in a state of 

 quiescence, or moving with a velocity not only six million, but several 

 million million times greater than that of light !" * 



Guyot. 1832. 



Another ingenious attack upon the " Problem,'* in a somewhat similar 

 though really distinct direction, was made by Dr. Jules Guyot — a 

 French physician, — in a very original and suggestive treatise entitled 

 Elements de Physique GeneraJe, Svo, published in Paris in 1S32, at 

 about the age of twenty-seven years. This writer seems to have had, 

 even at this early date, a general idea of correlating the physical forces. 



Assuming with other physicists, two kinds of matter, — one sensible in 

 the gaseous liquid and solid forms, the other insensible, in the " simple 

 elementary and atomic" condition of the aitherial medium^ filling all space 

 under a state of constant and enormous pressure, and infinitely more 

 subtile than any particle of combiuable matter, — and assuming also two 

 kinds of movement, one of translation and the other of vibration, Guyot 

 maintained that these two forms of motion are reciprocally comple- 

 mentary and convertible, their sum being constant. So that motion is 

 essential to matter, is equally indestructible, and is directly propor- 

 tional to its mass. He held that light, heat, sound, and the excitations 

 of smell and taste, are all the results of molecular motion or vibration, 

 as are also the agencies of electricity, magnetism, and gravitation. 



In a work on the pressures resulting from aerial motions, published 

 in 1835, Guyot records some curious experiments on the influence of 

 vibratory sounding bodies in causing light objects to approach them ; — 

 experiments which immediately recall the suggestions made by Dr. Rob- 

 ert Hooke more than a century and a half earlier, and which would cer- 

 tainly have delighted that philosopher. Disks of pith and of paper, 

 delicately suspended near a vibrating tuning-fork, were observed to be 



* Annals of Philosophy, new series, vol. i, p. 410. 



