2 1 S Image In flam Reflefttjrs. [Book III. 



QJR. will, after reflection, appear to have diverged 

 from q r. 



Every object placed before a reflecting furface has 

 its correfponding image. If the object is a plane 

 furface, the image will alfo be a fimilar plane furface ; 

 if the object is a curvilinear furface, the image will 

 correfpond to it ; and in all cafes it is found in this 

 manner, by perpendiculars drawn from the object 

 to the reflecting furface, or the reflecting furface pro- 

 duced. 



To fee any object, the eye muft be fo placed that 

 fome of the rays of light diverging from the object 

 juay fail upon the eye j and if, by looking upon a re- 

 flecting furface we fee an image, we Ihould, if our 

 judgment had not been corrected by experience, con- 

 ceive an object to be placed behind the furface from 

 which thefe rays diverged. Now, as an object may 

 be placed in fuc'h a fituation before the reflecting fur- 

 face that no rays can be reflected to our eyes, we 

 fhall not always fee an object by reflection, and the 

 places of the object, the fpectator, and the reflecting 

 furface, mufl be taken into consideration. Let QJR 

 be an object before the reflecting furface A B, q r its 

 image, as before (fig. 2.) and O the place of the fpec- 

 tator. Join O A, O B, and produce the lines O A, 

 OB indefinitely to T and P, unlefs the image lies 

 within the lines A T, B P the object will not be feen 

 by reflexion. Let/ without this fpace be the image 

 of F G, and join OfOg, and fmce thefe two lines do 

 not any where cut the reflecting furface, it is evident 

 that by looking on the furface we fhall not fee the ob- 

 ject. We fhall fee part of QJR, becaufe part of q r 

 lies within the fpace abovementioned, and to find the 

 part of QJl which is vifible by reflexion from the 

 point s, where O P cuts r, draw s S perpendicular 

 S t* 



