52 Remarks on Inertia. 



tion. The only reason we can give for its existence is this : 

 « Eiftev o $ i0 $, ywsaOa, xat tysvtto." We were surprised therefore 

 that Professor Farrar should give his countenance to such in- 

 vestigations ; and our astonishment was not lessened by his 

 conclusion as to the probability of his own theory.* The 

 learned Professor supposes that every body may be acted 

 upon, by an indefinite number of equal forces, in all possible 

 directions, and consequently the body remains at rest. Where 

 then an extended force is applied in any direction, it destroys 

 the efforts, or forces of the body, which act in a contrary di- 

 rection to the whole extent of its power ; and therefore the 

 forces of the body which have the same direction as the ex- 

 ternal force will no longer be balanced, and thus the body 

 will be pat in motion by them ; and its velocity will be pro- 

 portioned to the external force : since the efforts on one side 

 of the body being destroyed by the force to an amount ex- 

 actly equal to itself, those on the opposite side must be supe- 

 rior to the forces which before balanced them by an equal 

 quantity. We suppose it to be a corollary from this reason- 

 ing, that the forces which are constantly acting upon bodies 

 must be very powerful : for in proportion as we apply a great- 

 er force to any body, or in other words, as we destroy a lar- 

 ger amount of the forces which belong to that body, its velo- 

 city will be increased ; and if the theory be carried out, we 

 must conclude that this velocity is wholly caused by destroy- 

 ing the equilibrium of the equal and opposite forces : — 

 nearly in the same manner as a body is put in motion by the 

 pressure of the air on one of its surfaces, when the atmos- 

 pheric pressure is removed from the opposite surface. Now, 

 however ingenious this explanation of what may be the cause 

 of inertia, appears, we would inquire, with all deference 

 to the learned Professor, whether there would not be more 

 light on the subject to every understanding from saying, sim- 

 ply, that matter is wholly passive ; and therefore to cause 

 motion in a body which is at rest, a force must be exerted ; 

 and also that the body's velocity will be exactly proportion- 

 ate to the force impressed. We believe that this is all that is 

 known with respect to the inertia of matter, and the commu- 



* " We do not pretend to decide whether the resistance which hodies oppose 

 to motion, does or does not arise from a cause of this kind." — Cambridge Me- 

 chanics, p. 179. 



