OF OPTICS. 



267 



which proves that he sees not the real object, but its 

 image. This is also confirmed by means of the small 

 mirror L in the reflecting telescope, which is made of 

 opaque metal, and stands directly between the eye and 

 the object towards which the telescope is turned ; and 

 will hide the whole object from the eye at e, if the two 

 glasses R and S are taken out of the tube. 



The multiplying glass is made by grinding down the Th 

 round side h i k of a convex glass A B, into several fla 

 surfaces, as h b,bld,dk. 

 An object C will not ap- 

 pear magnified, when seen 

 through this glass, by 

 the eye at H ; but it will 

 appear multiplied into as 

 many different objects as 

 the glass contains plane 

 surfaces. For, since rays 

 will flow from the object 

 C to all parts of the glass, 

 and each plane surface 



will refract these rays to the eye, the same object will 

 appear to the eye, in the direction of the rays which en- 

 ter it through each surface. Thus, a ray g i H, falling 

 perpendicularly on the middle surface, will go through 

 the glass to the eye without suffering any refraction ; 

 and will therefore shew the object in its true place at 

 C . whilst a ray a b flowing from the same object, and 

 falling obliquely on the plane surface b h. will be re- 

 fracted in the direction b e, by passing through the glass ; 

 and upon leaving it, will go on to the eye in the direc- 

 tion e H ; which will cause the same object C to appear 

 also at E, in the direction of the ray He, produced in 

 the right line He n. And the ray c d, flowing from the 

 object C, and falling obliquely on the plane surface d k, 

 will be refracted (by passing through the glass and 

 leaving it at/) to the eye at H ; which will cause the 



LECT. 



VII. 



