40 GORHAM, ON THE MAGNIFYING 



each of which lying side by side in a linear direction will 

 produce exactly such a series of overlapping circles at the 



Fig. 10. 



bottom of the eye (fig. 11). Hence a small, narrow, transparent 

 slit for the transmission of light when brought very near to 

 the organ of vision, forms an image not of a line but of a 

 plane rounded at either extremity. 



3 The area of the aperture appears to be traversed Ly longi- 

 tudival dark hands. — " If we hold the hand between the eye 

 and a bright cloud, or the ground-glass of a lighted lamp, and 

 open tlie fingers so as to admit the smallest portion of light, 

 we shall perceive similar dark bands intersecting the luminous 

 space at regular intervals." * The explanation of this phe- 

 nomenon is founded on the interference of light, which, 

 according to the undulatory theory, takes place when the un- 

 dulations meet in opposite phases : these being superposed 

 produce darkness. 



We have now to examine the appearance of bodies held 

 close to the eye, and in the light admitted through small 

 linear apertui'cs such as we have been describing, 

 * See Woodward, on ' Polarized Light.' 



