_Messrs. Swift’s Microscopes_ have a well-established reputation for quality and good workmanship, and therefore can in no way suffer by comparison when placed beside those of other opticians. One of the characteristics of Messrs. Swift’s microscopes--and this runs through the whole series--is that they are all made to a _standard_ gauge, so that the several parts of the instruments, as well as their accessories, are interchangeable; the cheaper forms, with those of the first quality and finish. Should the student, then, start with a No. 1 model, he can at any time build it up, as it were, with the accessories designed for a No. 3 or 4, that is, for an instrument of double the price he started with. The optical centre is preserved throughout the whole series of microscopes. [Illustration: Fig. 81.--Swinging Leg Attachment of Swift & Son’s Four-Legged Microscope Stand.] The tripod foot has, it appears, taken the place of some of their other forms of instruments, while their four-legged _tripod_, if it can be so designated, is a novelty of quite an unusual character. The swing leg is attached to the framework of the tripod by the screw (Fig. A), which is provided with a powerful steel spiral spring, compressed between two steel collets when the screw is driven home, as shown in Fig. B. The expansion of this spring will obviously take up and compensate automatically any wear and tear that is likely to occur between the bearing surfaces, and it is therefore impossible for the fitting to get loose. _Swift’s Four-legged Microscope_ (Fig. 80) is one possessing great stability in whatever position it may be placed; the body being supported on a horse-shoe platform, from which its four legs spring, the two front legs being fixed, while the hind legs are pivoted to the platform. This arrangement of pivoting the hind legs enables the microscope to adapt itself to any uneven surface, thus keeping it always in a steady position, while it also reduces the danger of being upset by any lateral movement of an accidental nature. The feet are studded with corks, an additional aid to steadiness and fixity for microphotography. The length of the body from the ocular to the nose-piece is 6-1/2 inches, and can be extended to 9 or 10 inches by means of the draw-tube, which has a millimetre graduation. The stage, which is of horse-shoe shape, is provided with spring clips, to which a movable mechanical stage can at any time be attached. The sub-stage partakes of two forms, one being an ordinary fitting, taking an ordinary condenser; the other, the regular rack and pinion achromatic condenser with centring adjustments. It has a diagonal rack and pinion coarse adjustment, the fine adjustment being made by micrometer screw of the finest character. [Illustration: Fig. 82.--Swift’s Spiral Rack and Pinion Coarse Adjustment.]