V

4 °

Sir Is'AAc Newton’s Book!

a I. Farther, a power may be fo applied to a movingbody, as to ad obliquely to the motion of the body. Andthe effects of fuch an oblique motion may be deduced fromthis obfervation.; that as all bodies are continually moving a-long with the earth, we fee that the vifible effeds of the famepower are always the lame, in whatever diredion the powerads: and therefore the vifible effeds of any power upon abody, which feems only to be at reft, is always to appearancethe fame as the real effed would be upon a body truly at reft.Now fuppofe a body were moving along the line AB (infig. l.) and the eye accompanied it with an equal motion inthe line C D equidiftant from A B ; fo that when the body isat A, the eye fhall be at C, and when the body is advanced toE in the line AB, the eye fhall be advanced to F in the lineC D, the diftances A E and C F being equal. It is evident,that here the body will appear to the eye to be at reft ; andthe line FEG drawn, from the eye through the body fhall feetnto the eye to be immoveable; though as the body and eyemove forward together, this line fhall really alfo move ; fothat when the body fhall be advanced to H and the eye to K,the line FEG fhall be transferred into the fttuation KHL,this line KFIL being equidiftant from FEG. Now if the bo-dy when at E were to receive an impulfe in the diredion ofthe line FEG; while the eye is moving on from F to I, andcarrying along with it the line FEG, the body will appear tothe eye to move along this line FEG: for this is what has juftnow been faid ; that while bodies are moving along with theearth, and the fpedator’s eye partakes of the fame motion,the effed of any power upon the body will appear to be what

it