268 The American Naturalist. [March, 
steady character and its low temperature. The burner with its glass 
chimney is enclosed in a cylindrical mantel constructed of brass and. 
sheet iron, in which are inserted two horizontal tubes perpendicular to 
one another and at the level of the brightest part of the light. One 
of these tubes serves to illumine the signal, while through the medium 
of an arm carrying a mirror on a universal joint the light from the 
other tube may be thrown at will on the crystal, the vernier, or the 
paper. 
Darkening Attachment for the Goniometer.—Traube’ has 
devised a very simple attachment for the Fuess goniometer with hori- 
zontal circle by means of which the crystal under measurement is pro- 
tected from all light except that which comes from the collimator. 
The attachment is easily adjusted and quickly removed, and is so 
effective that measurements may be made at any hour of the day in an 
undarkened room. The frequent alternation of light and darkness 
which is so trying to the eye can thus be avoided. 
Lecture Microscope.—Fuess® has designed a simple form of 
petrographical microscope adapted to the lecture room, where it can 
be passed from hand to hand by the students. With full set of acces- 
sories the instrument costs in Germany 158 marks. 
Czapski’s Ocular.—Czapski’ considers the attachments on petro- 
graphical microscopes which have been devised for quickly changing 
from parallel to convergent polarized light, as quite unnecessary com- 
plications of the instrument, since the same results can be obtained by 
the use of the modern iris diaphragm below the condenser. To observe 
the interference figure of a very small crystal which only partially 
covers the field of the microscope, Czapski’s method is to bring the 
crystal as near as possible to the middle of the field, remove the ocular, 
and place a diaphragm with small aperture over the microscope tube. 
With the aid of a weak lens one sees within this aperture the real 
image of the crystal. The crystal is now brought more accurately to 
the centre so that it occupies all of the now diminished field. Remov- 
ing the lens one sees the best possible interference figure from the erys- 
tal. 
He has devised specially for this work an ocular with an iris dia- 
phragm at its lower end and an easily removable lens or a Ramsden’s 
ocular above. 
T Neues Jahrb. f. Mineral., etc., 1894, (ii), pp. 1-2. 
5 Neues. Jahrb. f. Misesl, ete., 1894, (ii). 
* Zeitsch. f. Kryst., xxii, pp. 158-162, 1894. 
