Fig. 162.—Glass Holder for carrying Coloured Glasses.
Watson’s lamp ([Fig. 161]) has a metal chimney, and is somewhat simpler in structure than those already referred to. For the student, the simpler and cheaper form will answer every purpose. A glass holder for carrying various tinted slips of coloured glass to act as a screen or modifier of the light is much employed, and assists in determining fine structures ([Fig. 162]).
Nose-pieces and Objective Changers.
A convenient appendage to the microscope is the rotating nose-piece, invented by Mr. Charles Brooke, F.R.S., and intended to carry two or more objectives, whereby a saving of time is effected, and the trouble of repeatedly screwing and unscrewing is avoided. In the application of the nose-piece attention should be given to centring. Messrs. Baker’s objective changer is intended to facilitate the placing and replacing the nose-piece in position. This adaptation consists of a milled head, acting on three jaws, having a universal screw thread, a decided improvement on the screw. Zeiss has adopted a tube-sliding objective changer with centring adjustments. Messrs. Watson met the difficulty of centring by making the nose-piece a part of the body-tube of their microscopes ([Fig. 163]). This, when adapted to the shorter body of the students’ microscope, fully compensates for want of length.
Fig. 163.—Watson’s Centring Nose-piece of Microscope.
Their triple nose-piece is constructed with much care, and when in use is found very effective. It is manufactured of that very light metal aluminium, and which minimises the strain produced by the heavier brass nose-piece.
Finders.—The finder affords a necessary and useful means of registering the position of any particular object, so that it may be readily found again at any subsequent period. In the work of examination the finder will save time when making a special research, extending over a considerable surface.
