STALLO'S " CONCEPTS OF MODERN FHYSCIS." 235 



merely a fiction of the imagination, still the presentation of one can do no possi- 

 ble harm and will do some good by tending to keep the distant action philosophers 

 from saying things they may ere long be heartily ashamed of. Mr.Wm. B.Taylor, 

 of Washington, in the Smithsonian Report for 1876, pp. 205 to 282, gives brief 

 descriptions of the Kinetic theories of Newton, Hooke, Villemot, Bernoulli, Le 

 Sage, Euler, Herapath, Guyot, Faraday, Sequin, Bouchepom, Lami, Waterson, 

 Challis, Glennie, Keller, Tait, Saigey, CroU, Leray, Boisbaudron, Guthrie and 

 Crookes. None of these answer the conditions. Mr. Taylor resorts to actio in 

 distans. On page 211 he gives the six following conditions to which a theory of 

 gravity must correspond or be rejected at once : 



ist. " Its rt'/r^<r^'/(9« is radial toward the acting mass, or rectilinear — indefi- 

 nitely. This rectilinear traction is incapable of deflection by any intermediate 

 force. It suffers neither disturbance nor interference from any multiplication of 

 similar lines of action, and admits neither of reflection, refraction, nor of compo- 

 sition. 



2. '■'■li^ quantity is exactly proportional to the acting mass — indefinitely. 

 Corollary : hence, 2b. Its integrity of action is complete with every accumulation 

 of additional demand — indefinitely ; that is to say, no multiplication of duty in 

 the 5-lightest degree impairs its previous tensions. 



3. "Its intensity is diminished by recession, in proportion to the square of 

 the distance through which it acts — indefinitely ; in a manner somewhat analogous 

 to — but (as modified by the second condition,) radically different from — the action 

 of light. 



4. " Its time of action is instantaneous throughout all ascertained distances, 

 and therefore presumably — indefinitely. Corollary : hence, 4b. Its rate of ac- 

 tion (if the expression may be tolerated) is precisely the same on bodies at all 

 velocities — indefinitely. It no more lags on a comet approaching the sun, at the 

 inconceivable speed of 200 miles in one second than on a body at the lowest rate 

 of motion, or than on the same comet receding from the sun at the same velocity. 



5. ^ ^ lis quality is invariable under all circumstances — indefinitely. Jt is 

 entirely unaffected by the interposition of any material screen, whatever its char- 

 acter or extent ; or in other words it can neither be checked by any insulator nor 

 retarded by any obstruction. 



6. " Its ^;Z(fr^y is unchangeable in time, certainly for the past 2000 years; 

 presumably — indefinitely. Corollary : hence, 6b. Its activity is incessant and 

 inexhaustible — indefinitely; the ceaseless fall of planets from their tangential 

 impulscD involving no dynamic expenditure in the sun or in other known matter." 



True to the mechanical theory the explanation about to be offered begins with 

 atoms. These atoms, however, are very active little things and not at all hard. 

 They were first introduced to the world as probably performing some such func- 

 tion, by Prof. Sir Wm. Thompson, of Glasgow, Scotland. They are the voriex 

 atoms that we heard so much about a few years ago. Helmholtz has shown that 

 vortices in a perfectly frictionless fluid would be eternal, Thompson experiment- 



