AN EXPERIMENTAL INVESTIGATION OF THE RELATION BE- 
TWEEN THE APERTURE OF A TELESCOPE AND THE 
QUALITY OF THE IMAGE OBTAINED BY IT. 
By Fred Vorhies. 
The subject of telescopic vision wa,s presented to the scientific world 
a few years ago in a series of articles written by Dr. G. J. Stoney . 1 At 
that time Dr. Stoney discussed the proposition as applied to the vision 
of distant planets and drew the conclusion that astronomers were not 
able to detect certain details upon the planet Mars.. Since the appear- 
ance of this series of articles a considerable discussion has taken place 
but no definite conclusions have been drawn. 
With these things in mind I set up in one of the physics research 
laboratories of the State University, apparatus designed especially for 
the purpose of investigating the effects that we get when viewing an 
illuminated surface through telescopes of different apertures. It is 
understood that the focal length of the lens is not important if the 
magnification is sufficient. 
For the purpose of clearness and simplicity, I made the following 
assumption which I later proved, experimentally, to be correct. In look- 
ing at the planet Mars, or any illuminated surface the same effects are 
obtained, whether we illuminate the surface from in front with diffused 
light or whether we remove the object and place in its stead a trans- 
parent object with the same details painted upon it and illuminate this 
new object from behind. 
Taking it for granted that the above assumption is correct, let us 
imagine that the planet Mars is removed and in its place a transparent 
object is located. In order to simplify matters still more let us illuminate 
this transparent object from behind with a point source of light, in- 
stead of with an infinite number of point sources, as we have in diffused 
light. If we then imagine a large lens placed in front of this trans- 
parent object we shall be ready to consider the different effects that ap- 
pear. The lens is introduced for the purpose of analysis and has no 
effect on the image. This lens will focus the image at some definite 
point. If we should imagine this light after it has been focussed we 
would find that it consists of a central bright spot surrounded by a 
Philosophical Magazine vol. 16, 1908. 
