Microscopy; The Construction, Theory and Use of the Microscope

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 edition. Excerpt: ... off duty, so that, although it is prevented seeing anything, it is not kept shut. It is best, as we have said, to keep it open; but when doing so the observer, in addition, should try to make it turn as if it were looking at the object seen by tlie eye in use. By this means an unconscious similarity in the focussing is brought about at one and the same moment. If, however, the observer lets his "off-duty" eye simply become a blank, then this focussing is not effected, and it may be that a certain kind of diplopia (double sight) may be brought about by this means, which is very unpleasant; for the effect is that the observer, after leaving the microscope, apparently sees double, even, perhaps, for an hour afterwards. For those unable to learn to do what we have said, a neat little arrangement is made to fix on to the draw-tube that holds a small shield, effectually cutting off "the seeing" of the eye not in use. Some users of the microscope regularly employ this ingenious little piece of apparatus. It consists of two parts, as shown in Fig. 130, jointed in the middle; one part has in it a circular aperture, which slides over the draw-tube of the microscope, and the other shuts out light from the disengaged eye. It is usually made in vulcanite, in two sizes, one for the Continental, and the other for the English size draw-tube. The Position the Verniers should Occupy and the Method of Centring a Circular Stage If a 3 x 1-in. ordinary glass slip be taken and its centre marked with a dot of ink, this dot should be exactly i in. from either end and in. from either side. This may be called the centre of the slip. If a cover-glass be taken with a circular diatom, such as an Aulocodiscus Brunii burnt on to it, ...