3(5 GORHAM, ON THE MAGNIFYING 



Tiie experiments illustrative oi" these curious phenomena in 

 which the li^ht becomes bent into hyperbolic curves when 

 passing near the edges of bodies, present nothing in common 

 with those which form the subject of the present paper, in 

 which tlie short space which is caused to intervene between 

 the eye and the light precludes the possibility of detecting 

 the coloured fringes, supposing indeed tliat these were the ob- 

 jects of which we wei'e in search. The only point of resem- 

 blance between them consists in tlie minuteness of the aper- 

 tures through which the light is admitted, and this serves to 

 show that by the same simple means different ends may be 

 accomplished. The mere peeping through a pin-hole without 

 some definite purpose, — some object to be examined, — some 

 particular theory to be investigated, were indeed a childish oc- 

 cupation. It is more than probable that some of the followers 

 of Newton were not much better engaged when we find the 

 celebrated Goethe afterwards using the words, si per foramen 

 exifpium, somewhat tauntingly in referenc e to the fact of their 

 so frequently introducing tliis term into their writings. 



The curious figures now about to be described, and which 

 are produced by tlie transmission of light through minute 

 narrow apertures, although related to those whicli have been 

 shown to result from mere perforation, contrast with them, 

 nevertheless, in several important particulars, of which not the 

 least striking, is the production of quadrangular planes which 

 are formed when the light is partially intercepted during its 

 passage towards the eye, and which when multiplied by in- 

 creasing the number of lines which produce them, appear to 

 fall together at their edges, and so to resemble hollow semi- 

 transparent figures of considerable beauty. 



It may not be withheld, however, that this part of our sub- 

 ject is, so far as 1 have yet proceeded, circumscribed within 

 narrow limits, being restricted chiefly to the formation of 

 images on the retina of the eye, of those solids known as paral- 

 lelopipeds, with composite forms, resulting from the multipli- 

 cation of the simple ones. The peculiar feature in the experi- 

 ments, consisting not so much in the novelty of the forms 

 themselves, as in their mode of production. 



We proceed to consider the phenomena which light presents 

 when introduced through a narrow aperture held at a short 

 interval of an inch or two from the eye. 



When an exceedingly small transparent space or aperture* 



* Lines for this purpose maybe drawn on glass, or cut through tin-foil. 

 When the former process is adopted, a small round disc of Indian ink is 

 laid on a circular piece of very thin glass, such as is used for the cover of 

 microscopic objects, and whicli may be procured of any microscope makei-. 



