Dr. North on the Angle of Aperture in Microscopes. 225 
When it is confirme the micrometer. 
It is obvious that as the image of a faint star in the telescope, 
So Is an indivisible point or line in the image forme h 
Magnifier, or with the unaided eye, illuminates a tissue with as 
much light as possible, often employing two condensers of artifi- 
cial light, yet as the brightness of an image is diminished in in- 
Verse proportion to the square of the linear magnifying power, 
an ultimate fibrilla of voluntary muscle, when magnified 1000 
diameters (and as much or more amplification is needed ), would 
ve only ,.,1,,;th part the light on its image, were it not for 
the large aperture of the objective. Saag 
Witha microscope just as with a single eye, we judge of depth 
and form, by means of geometrical foreshortening and infinitely 
delicate gradatiouis of light, shade, and sometimes color ; assisting 
our conclusions by change of focus and directing attention to 
different parts and presentations. Nothing shows more strikingly 
: recogn 
Stooxp Senizs, Vol. XVII, No. 60.—March, 1854. 29 
