34 GORHAM, ON THE MAGNIFYING 



But when these lateral superfluous rays are excluded by 

 usino^ a divertjent pencil of light only, as in the diascope, the 

 shadow becomes visible ; and not only is the exposed portion 

 of the body of the needle seen, but its eye is well defined, and 

 both appear considerably magnified (fig. 8). 



Hence we may safely assume that all small bodies, whether 

 transparent or opaque, are undistinguishable when held close 

 to the naked eye, in broad day-light, or diffused light of any 

 kind, but that if it were possible to distinguish them while in 

 this position, they would appear magnified ; and moreover, 

 that this may actually be effected in many instances by the 

 artificial contrivances to which we have been endeavouring to 

 direct attention. 



Fig. 8. 



If a single object be retained in a given position before a 

 screen, it will intercept the rays emitted from any number of 

 separate luminous bodies, or sources of light, situated in front 

 of it, and so cast as many shadows. In this way the shadows 

 are multiphecL Thus if a finger be held within an inch or two 

 of the wall, and a number of tapers at as many yards, the pencils 

 of light from the tapers crossing the finger in different direc- 

 tions, and being intercepted by it, an equal number of shadows 

 are cast on the wall at intervals, related to the position of the 



