700 MICROSCOPY. 
light be made to pass through the narrow ring of clear aperture 
remaining around the stop; but if water be flowed in both above 
and below the balsam-mounted object, converting both the objec- 
tive and the illuminating semi-cylinder into immersion arrange- 
ments, a well lighted and defined image is immediately produced. 
With regard to extreme angles in connection with dry objects, Mr. 
Tolles claims that his much-disputed 4 inch does actually form an 
image with the most oblique rays that can impinge upon the slide, 
all other rays being cut off by a card or shutter which can be 
moved up close to the bottom of the slide. 
A FINDER FOR MICROSCOPES WİTH PLAIN STAGE.—À writer in 
“ Science Gossip” advises a horizontal line ruled across the centre 
of the stage from side to side. Vertical lines are ruled across this 
an inch each side of the centre. A large label, say nine-tenths of 
an inch square, is fixed to each end of the slide: When the ob- 
ject is in position these labels are marked with lines or dots to 
correspond with the stage-lines below, and by these can easily be 
returned to the same position on the same stage or any stage ruled 
exactly to match. Several objects may be indicated on the same 
slide by as many marks, and a memorandum preserved recording 
which marks indicate each object; thus 4-7 or 4 records that the 
object is indicated by the fourth vertical and the seventh horl- 
zontal dot or line. 
Tue RIGHT-ANGLED Prism AS A SUBSTITUTE FOR THE MIRROR FOR 
TRANSMITTED LIGHT .— Mr. Ingpen uses an achromatic doublet, 
plano-convex, which can be placed when desired close to one side 
of the right-angled prism for transparent illumination, thus mak- 
ing the prism available as a substitute for both plane and concave 
mirrors, while the usual form where the condensing lenses are 
balsamed to the prism is useless for giving parallel light. 
- APPARATUS FOR GIVING PRESSURE TO OBJECTS WHILE DRYING: 
Though spring clips of various kinds are chiefly employed for - 
purpose, yet a more compact and controllable arrangement 18 
sometimes preferred. A mounting board is often arranged to 20" 
the slides while pressure-rods tipped with cork rest upon the oor 
glasses and give the required pressure ; these rods being held in = 
vertical position by being passed through loops of wire oF through 
a couple of perforated shelves one above the other, while à 
pulled down with the required degree of force by elastic | 
Set 
they re 
