120 THE MICROSCOPICAL NEWS. 
experience, the capacity of the most perfect objectives, the usual 
forms of illumination being assumed, is exhausted with an eight- 
fold angular amplification, so that every detail that can be pos- 
sibly delineated by an objective in its “ virtual” image is certainly 
accessible to any eye possessing normal vision, when the tube and 
ocular, taken together, represent a telescopic magnifying power 
of eight times. Even this performance is only reached in the 
case of low and middle power objectives; for when the focal 
length is less than } inch, the relative perfection of construction 
perceptibly fails, on account of the rapidly accumulating technical 
difficulties, and there certainly does not exist an objective of 
zs inch focus whose optical capacity exceeds a fivefold uugular 
amplification. 
From all this may be gathered how utterly futile any efforts to 
obtain disproportionately high amplifications by means of specially 
constructed eye-pieces must prove ; and, as regards any expectation 
of exalting the performance of the instrument by further shortening 
of the focal length of the objective, there stands in the way one 
objection, which, in the present state of our knowledge, is absolute 
and insuperable—namely, that the imperfections resulting from 
residual aberrations and defective technical manipulation increase 
with every addition of magnifying power. This form of diffraction, 
likewise, turns the image of each point in an object into a dispersive 
circle of greater or less diameter; but the resulting diminution of 
optical capacity, while scarcely noticeable in objectives of moderate 
power, compared with the effect of residual aberrations, becomes 
very serious with the higher powers. Assuming the magnitude of 
angle of aperture 180° in air, which cannot be exceeded beyond a 
few degrees, even by immersion systems, we find, e. g. for an 
amplification of 1000, the diameter=-, inch, and for amplifica- 
tion of 5000=54, inch, without reference to the mode in which 
the amplification is obtained (through objective and ocular). And 
if we would know what conditions are involved in such amplifica- 
tions—as, for instance, 5000 fold—we have only to make a 
puncture of ;4, inch diameter with a needle in a card or piece of 
tinfoil, and through this opening to look at some brightly illumi- 
nated object, which has well-defined edges (e. g. a candle flame), 
and we shall have before our eye of what must be the appearance 
of the outlines of a microscopic object magnified 5000 times, even 
if the microscope itself were absolutely perfect, the diffractive effect 
excepted.* 
Taking all these circumstances into consideration, it must be 
concluded that no material exaltation of the absolute power of the 
* Due to smallness of aperture of a minute lens, and to be carefully distin- 
guished from the diffraction which is caused by the strzcture of objects. 
