Note 24 — Chapter II · The Petrographical Microscope.[16]
Reading edition
In some microscopes the analyzer is in the form of a “cap” nicol, arranged to be fitted over the top of the eye-piece, and not introduced in the microscope tube as shown here. This form is not so convenient, as the “cap” nicol must be set by hand every time it is desired to make observations with crossed nicols. But at the same time it avoids any possible refocusing which may be necessary when the other type of analyzer is introduced in the tube.