stage by two strips which are undercut at 45° so as to overlap the top surface of the slide. The 
upper strip is capable of a small vertical movement, but is held against the surface of the stage 
by shoulder screws. The upper strip is raised, the slide is inserted and the strip then falls by its 
own weight and holds the slide down on to the lower strip and against the surface of the stage. 
The substage (7) is made on very massive lines as it is required to carry the double illuminator (q) 
which is of large size. It is focussed by means of the micrometer screw (7) which carries a divided 
circle reading to ‘01 m/m. The substage centring adjustments are actuated by the screws (s). 
The adjustments are by means of dovetail slides instead of the more usual arrangement which 
is not sufficiently rigid. The duplex substage illuminator is shown in Fig. 4, the central optical 
system is of quartz, the outer combination is of glass and forms the dark ground visual 
illuminator ; it is provided with an independent focussing adjustment. 
The focussing unit (k) consists of a box shaped block which can be slid along the slide (g) and 
clamped in a suitable position. Inside this block is a very accurately made floating slide which 
carries the object glass bracket (¢). The slide can be moved 1] c/m. by means of an extremely 
accurate micrometer screw with jewelled contact plates. The screw can be rotated direct by the 
handle (wu, Figs. 2 and 3) in which case one rotation of the handle moves the objective 1 m/m. 
A scale is fitted alongside the objective carrier (¢) divided in millimetres for coarse measurements. 
A small window is provided at (w) through which a dial fixed to the end of the micrometer screw 
can be seen. This is divided into 100 divisions, each division being equal to -01 m/m. motion of 
the objective. On moving the small lever (x, Fig. 2), an extremely accurate gearing is brought 
FIG 2 
ail 
Re). BECK.~ 
Loncon 
Beck Barnard ultra-violet microscope. 
Approx. { Size. 
6S 
