1896.] MICROSCOPICAL JOURIS^AL 15 



the larger hole. These rays of light, each having an 

 image-forming power when passing through a lens, are 

 all converged together to a focus, and the image formed 

 will, of course, be many times brighter than that of the 

 single ray which passed through the blackened card. 

 The lens then determines the place where the cones of 

 diverging rays from an object shall begin to converge, 

 and its position marks the place where refraction occurs, 

 and also marks the point where the rays cross and invert 

 the image. So the objective only converges and com- 

 bines masses of rays, each one of which has the power 

 of forming an image. It it thus obvious that the in- 

 creased aperture of a lens means greater illumination. As 

 stated before. Dr. Goring found better resolution with 

 an unachromatized combination of large aperture than 

 with an achromatic system of small aperture. 



The relation between aperture and resolution was 

 shown by a simple experiment of Lord Raleigh. Each 

 person was furnished with the apparatus required. It 

 consisted of a piece of fine wire gauze, and a black card 

 with two pinholes, one very small, and the other made 

 with a thick pin. Holding the gauze to the light and 

 looking at it through the small pinhole, gradually mov- 

 ing it further off, at a certain distance the meshes would 

 become invisible. Moving the card along till the larger 

 pinhole was in front and close to the eye, instantly the 

 meshes would become visible again. It will be seen at 

 once that the greater aperture allowed to the eye brought 

 them into view. 



That it was not merely more light that brought the 

 image of the meshes distinctly to the eye can instantly 

 be proved by another simple experiment. Get a piece of 

 blackened glass, and make two scratches on it about 1-16 

 of an inch long, one vertical and the other horizontal. 

 Hold the gauze so that the wires are horizontal and ver- 



