Slide-holder for the Microscope.
heavier forming the stage plate ; further description seems scarcely needed. With many objects it is absolutely necessary to have them in a certain position with respect to the light to
see them at all, and with many more a slight change in position renders them far more distinct, and I am led to think that in such cases this slide-holder will be found both con venient and useful from the ease with which a slide placed upon it can be completely rotated ; it might also be found useful in some cases of examining transparent objects by oblique light, and the hole in the lower plate might be made oblong, so as not to interfere with the oblique rays from the
mirror.
A second and more general use to which this slide-holder might be applied is that of a selenite-holder for use with the polarizing prisms. In the ' Microscopical Journal' for July,
1860, pp. 203-4, I described a simple form of selenite stage having for its object a means of removing and replacing again the various selenites without disturbing the slide under exami
nation or requiring to alter the focus of the microscope. In the revolving stage plate I now bring under the notice of the Society, it will I think be seen that by means of the in tervening space between the lower and secondary plates, as shown in a, drawing b, the selenite plates can be slipped in and out without disturbing the object ; and in the case of this holder there is the additional advantage obtained of having the object itself revolvable, while the polarizing prisms and the selenites remain in a fixed position with regard to each other— an arrangement which brings out some remarkable effects. It will also be apparent that when this secondary stage is used with a microscope that has a revolving stage plate of its own, the selenite plate and object under examination may be made to rotate in the same or in an opposite direction to one another ; while the polarizing prisms remain fixed.