238 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
mineral to abrasion by diamond : this is the property measured. The 
instrument (plates III. and 1Y.) consists of the following parts : — 
1. A standard and apparatus for adjusting to Microscope. 
(i) foot adjustments ; (ii) rotating adjustments ; (iii) lifting 
adjustments ; (iv) fixing adjustments. 
2. A balance beam and its yoke. 
3. A rotary diamond in its end. 
4. Apparatus for rotating uniformly. 
5. Apparatus for recording rotations. 
6. Apparatus for locking and releasing. 
7. Apparatus for recording depth. 
The instrument admits of measurements with any of the four vari- 
ables, — rate, weight, depth, duration. The last has been found most 
practical, because it gives the highest values, and hence admits of the 
most delicate gradation. 
Weights (e.g. 10 grm.) are placed on the pans iv (plate IV.), and a 
micrometer scale at m; D is the diamond, which has to be carefully se- 
lected, and has a perfect point. The plate m is rotary on a horizontally 
pivoted ring, so that it may be turned in any azimuth. This device is so 
adjusted that the micrometer scale is visible in the field of the Microscope 
at the point exactly 10 mm. from the axis of rotation of the diamond point ; 
this is one-sixth of the distance from the diamond axis to the beam pivots 
a, hence any downward movement at the diamond point is magnified by 
one-sixth at the micrometer. The reading is therefore seven-sixths of 
the actual depth bored. If now it be rotated until the micrometer scale 
stands at right angles to the beam, and be then tipped gently, an inclina- 
tion may be found where, under a high power, only one line of the 
micrometer scale is in focus at a time, and a downward focus of precisely 
• 01 mm. is necessary to bring the next lower line on the slope into 
focus. Conversely, if we focus on the lower line and allow the diamond 
to bore its way down *01 mm., the next 
higher line of the micrometer glass will come 
into sharp focus only when that depth is 
reached. We thus have here an extremely 
sensitive measure of depth. 
The author gives a preliminary series of 
tests with the minerals of the Molis scale to 
show the efficacy of the method. The im- 
provement of certain details is under con- 
sideration. The instrument seems to be 
applicable to the determination of the amount 
of double refraction, and to the measurement 
of the thickness of mineral thin sections. 
Immersion - Oil Bottle.* — Dr. W. Greb- 
hardt describes a new form of bottle for hold- 
ing cedar oil for immersion purposes. As the 
illustration (fig. 39) shows, the bottle is much like a small Erlenmayer’s 
ask with a side tube S and a fairly broad neck T, the latter being 
* Zeitschr. f. wiss. Mikr., xiv. (1897) pp. 348-50 (1 fig.), f 
