The Microscope and its Misinterpretations. By J. Michels. 53 
all its stages ; but wten the causes are well understood, the diffi- 
culties are reduced to a minimum, and even turned to account in 
the examination of difficult objects. 
Grreat success in the use of the microscope can only be obtained 
by the skilful manipulation of the light, and he that is not ac- 
quainted with the numerous schemes, devices, and contrivances in 
its management, might as well be in the dark ; no directions here 
avail, and nothing but diligent and constant practice will render the 
student efficient in this respect. 
I once stood an hour watching a leading London optician 
struggling to show me the true markings of a diatom with a new 
object-glass he had recently constructed, with which he had had no 
previous difficulty. He at last gave up the attempt in despair. Of 
course an objective that has once performed a specific test will do so 
again. In this case the only thing in fault was the management of 
the light. This had disgraced the object-glass, and enraged its 
maker. 
In contrast with the above case I may mention the real pleasure 
I experienced in witnessing the skill of a professional microscopist 
of this country. In his hands all difficulties appeared to vanish, 
and he showed me one of the most difficult objects known, with 
marvellous promptitude. 
But to return to my subject. To enable the student to familiarize 
himself with the true power of the microscope, and to train his eyes 
to detect errors of vision, certain well-known test-objects are in 
general use, which are also convenient to test the quality and 
power of objectives. A favourite object of this class is the scale of 
the Podura, a minute insect, which dwells in remote nooks of dark 
and damp cellars, and similar localities. 
This scale is usually mounted dry, and when viewed under the 
compound microscope with suitable objectives, presents a surface 
studded with marks similar to the well-known note of excla- 
mation (!). 
This test-object has been for years the delight of microscopists 
possessing high powers, and a sharp definition of its peculiar 
markings, as above mentioned, was accepted as its true appearance 
and form. 
For twenty-five years this scale was under constant examination 
by every grade of microscopists, from the grandees of the Eoyal 
Microscopical Society to the humble tyro, without any new or 
special feature being noticed, when on November 10, 18t)9, Dr. 
(t. W. Eoyston-Pigott, F.K.M.S., read a paper " On High-Power 
Definition," befoi-e the Eoyal Microscopical Society, and surprised 
the members by stating that all these years they had been gazing 
at the Podura scale, but had never yet seen its true markings. 
Dr. Pigott's paper described very fully what he had discovered as 
