Bauhaus-Universität Weimar

The Sciopticon Manual, Explaining Lantern Projections in General and the Sciopticon Apparatus in Particular Including Magic Lantern Attachments, Experiments, Novelties, Colored and Photo-Transparencies, Mechanical Movements, etc.
Marcy, L. J.
whose flatness of field in the table microscope leaves noth¬ 
ing to be desired in that direction, are entirely unsatisfac¬ 
tory when used in the gas microscope. 
One of the most influential causes of this we shall notice 
presently, but we will here only remark that, as the result 
of a large experience, we have become convinced that one 
must be contented with a moderate amount of success in 
this direction, and not expect what is, at present, at all 
events, impossible. 
The second great defect that we encounter in the use of 
the microscopic lens for projection, is the irregularity of 
distribution of light upon the screen. 
By reason of this we may have a field of light with a 
small bright area at the centre, rapidly fading off into dark¬ 
ness, with no well-defined margin. 
The causes of this are, among others, the confusion or 
want of accurate concentration of the cone of rays from the 
condensers, and the smallness of the objective, causing it to 
cut off oblique or marginal rays more or less, according to 
their obliquity. To remedy this difficulty we can work in 
two directions. 
In the first place, we may improve the spherical correc¬ 
tion of the condensers, or the concentrated character of the 
source of light. The first of these improvements has 
already been carried to its practical limit in the best sort of 
condensers, and the second involves the use of the electric 
light or of sunlight. 
In the second place, any increase in the diameter of the 
microscopic lenses, without a corresponding increase in their 
actual length, insures a great gain as regards the equal 
illumination of the field. 
With this view alone, therefore, a simple uncorrected or 
single corrected microscopic lens, such as accompanies the 
regular gas or solar microscopic attachment made for the


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