ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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wave-length of the light passing through the slit. The light, after 
being diffused by a plate of finely ground glass, passes directly into 
the observing instrument — axial angle apparatus, goniometer or Micro- 
scope, &c. As a strong light is necessary, a lime-light lantern is used. 
Lens-Support, with Polarising Apparatus.* — Dr. C. Leiss describes 
an instrument for examining large mineral, rock and paleontological 
sections in polarised light, which is also useful for examining crystal 
groups, separating minerals, &c. ; it is made by Fuess after the designs 
of E. Kalkowsky. To the foot are hinged an illuminating mirror Sp, 
and a glass plate P, which acts as the polariser. The glass plate O, 
Fig. 8. 
which may be replaced by metal plates having suitable openings, carries 
the object. The lens can be moved about in a horizontal plane by 
means of an arm jointed at and s, and the rack and pinion T gives an 
extended range of vertical motion. The analysing nicol, a Glan- 
Thompson prism, fits over the lens, and a slot is provided for inserting 
a mica or gypsum plate. Two Steinlieil lenses, giving a large flat field 
and magnifying four and eight times, are supplied with the instrument. 
Thermostat heated by Mineral Oil for Paraffin Imbedding.f — 
Herr W. Karawaiew describes a thermostat devised by him, which is 
heated by petroleum or benzoline, and regulated automatically by elec- 
trical contact. When the temperature for which the apparatus is adjusted 
ascends above the desired degree, the mercury column of an air thermo- 
meter inserted in the interior of the thermostat rises until it comes into 
contact with a platinum point, thereby making a current which acts on 
an electro-magnet. The power of the magnet is exerted on a movable 
metallic plate, which is inserted between the source of heat and the 
bottom of the thermostat. In this way direct heating is prevented until, 
* Neues Jalirb. Mineral., i. (1897) pp. 81-2; and Zeitschr. ang. Mikr., ii. (1897) 
pp. 289-90. f Zeitschr. f. 'wise. ? T ’kr., xiii. (1896) pp. 289-99 (3 figs.). 
M 2 
