606 
SUMMARY OF CURRENT RESEARCHES. 
of 45° with the cross-hairs, as before. Push in the wedge with its axis 
of least elasticity perpendicular to the arcs, or parallel to the line joining 
the hyperbola eyes. If the lemniscate arcs move in towards the centre 
of the field with their convex side forwards, the mineral is positive. 
Push in the wedge with its axis of least elasticity tangent to the arcs, 
or perpendicular to the line joining the vertices. If the arcs then move 
in with their convex side forwards, the mineral is negative. If the arcs 
move outwards with their concave side forwards, the mineral in the first 
position of the wedge is negative, and in the second position positive. 
(c) If the distance between the hyperbola eyes is not so great but 
that they lie within the field of view’, the mica and gypsum plates can 
both be employed to determine the positive and negative characters 
when the lemniscate figure is placed as before, with the line joining the 
hyperbola eyes forming an angle of 45° with the cross-hairs of the eye- 
piece. Insert either the mica plate with its axis of least elasticity 
parallel to the chosen line, or else insert the gypsum plate with its axis 
of least elasticity perpendicular to the chosen line. With either plate 
in this position, the arcs on one side of the hyperbola eyes will enlarge 
and those on the other side contract. If the arcs that lie on the inside 
of the eyes, or nearest the centre of the figure, enlarge, and those on 
the outside contract, the mineral is positive. On the other hand, if the 
arcs nearest the centre contract, and the outside arcs expand, the mineral 
is negative. This method can be used with plates that have too great 
an axial divergence for their determination when the unsymmetrical 
cross is placed with its arms parallel to the cross-hairs.” 
Microscopical Water Analysis.* — Herr C. Mez’s introduction to 
the examination of water deals principally with drinking water and 
sewage. The first part treats of the vegetable and animal organisms 
ordinarily found in impure water, and the second and larger portion of 
the work deals with the methods of microscopical analysis. 
One of the chief merits of the work consists in an attempt to introduce 
a simplified nomenclature : thus, Diplococcus flavus liquefaciens tardus , 
Micrococcus pyogenes albus, Bacterium fluorescens liquefaciens minulissi- 
mum , are designated M. flavovirens, M. pyoalbus, B. minutissimum. 
Cleaning Slides intended for Water-stuck Sections.^ — M. J. G. de 
Groot declares that the following procedure is absolutely perfect for 
cleaning slides intended to be used for sections which are to be stuck on 
by the water method. On a clean cloth is spread a little common chalk, 
and the cloth having been moistened with a drop of w'ater, the slide is 
rubbed therewith. The slide is again rubbed with a clean cloth moist- 
ened with water, and is then ready for use. 
* Biol. Centralbl., xviii. (1898) pp. 507-9. Hedwigia, xxxvii. (1898) pp. 96-7. 
I Zeitschr. f. wiss. Mikr., xv. (1898) pp. 62-3. 
