Fig. 77.—Watson’s Improved “Van Heurck Bacteriological” Microscope.
The Stage.—A somewhat new design has been used in building this up so as to reduce vibration to a minimum. The bracket carrying the stage, instead of being screwed on to the front of the limb, as is usually done, is made in a solid casting, taking the sub-stage beneath, and passing into the joint at the top of the foot. The joint bolt goes through the whole (limb and stage bracket), rendering the limb stage and sub-stage as firm as if it were one piece; a point of considerable importance.
The mirrors, which are plain and concave, are mounted on a swing arm, so that they may be turned aside when direct illumination of the object is required. On the right hand side also there is a steel clamping bar for fixing the microscope at any angle of inclination. The tripod foot, which has superseded most other forms, is adopted. At the points of contact with the table the feet are provided with cork pads, which give increased firmness and prevent vibration to some extent.
The sub-stage is provided with a fine adjustment of similar design to that employed for the focussing of the objective. It has become needful to embody such a refinement, in order that sub-stage condensers of large aperture, such as are in constant use for critical high-power work, may be adjusted with the same facility and precision as the objective—they, in fact, require it if the best work is to be got out of them. No pains have been spared by Messrs. Watson to render it absolutely perfect.
Watson’s Portable Microscope.—This instrument is similar in general detail to the Histological Microscope, but the foot, mirror stem, &c., are made to fold up in exceedingly compact form, and when set up for use the stand is perfectly rigid. Portable microscopes are, as a rule, but makeshifts. This, however, is a thoroughly sound, practical instrument and capable of best work with the highest power objectives, having good adjustments and universal size fittings throughout, so that the objectives and apparatus made for the larger instruments can be employed with it.
Fig. 78.—Watson’s Portable Microscope. Height of instrument when placed vertically and racked down is 93⁄8 inches.
Watson’s Petrological Microscope ([Fig. 79]) is a modification of their Edinburgh Students’ pattern, and designed specially for petrological and mineralogical work.
