ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 405 



Substage Illumination.* — S. 0. Akehurst urges the convenience of 

 employing annular light with objectives of high aperature, the annular 

 light being obtained by the use of a concentric reflecting condenser. 

 By this means there is no chromatic dispersion, and the spherical aberra- 

 tion is reduced to a minimum. Moreover, with the reflecting condenser 

 there is no loss of high-angle rays, because the excess of light is modified 

 by stopping out a portion of the central or dioptric beam ; hence the 

 fullest possible advantage can be taken of the N.A. aperture of the whole 

 optical system. The absence of chromatic dispersion results in a pure 

 image and in the possible application of photomicrography to critical 

 work. The author gives photographs of Pleurosigma angulatum and 

 other well known diatoms, taken with annular illumination under magni- 

 fications, in some cases, as high as 3000 diam. 



New Microscope Illuminators.! — F. Levy describes two forms of 

 illuminators which he has found satisfactory. The first, is adapted for 

 illuminating a Microscope hall, and consists of a centrally placed 2000- 

 candle Osram half-watt lamp in a hemispherical milk-glass globe. The 

 glass should have a slightly bluish tinge. Such a lamp should be 

 placed about 2 m. above the work-tables, and would suffice for one 

 hundred Microscopes. 



His second lamp is for individual use with high-powers in a labora- 

 tory, and consists of a special Osram lamp with wavy metal filaments of 

 100 candle-power. The front side of the globe is matted ; the rear side 

 mirrored. The lamp is enclosed in a frame in such a manner that the 

 greater part of the light falls on the Microscope mirror. The frame is 

 provided with grooves for the insertion of filter or matt disks. Near 

 the grooves openings are left so that the working space may be illumin- 

 ated without blinding the worker. 



Application of Direct Coolers to Projection.! — O. Zoth points out 

 the inconveniences of those forms of coolers which are operated by water 

 straight from the water-main. In such cases the water is under pressure, 

 and there is considerable risk of cracking, bursting, or loosening the 

 cover-glass. The author finds it better to use water at a pressure less 

 than the atmospheric. He accomplishes this by means of a siphon 

 arrangement, at the highest point of which is the cooling chamber. By 

 means of a tube the chamber is connected with a large trough of water, 

 iced if necessary, under the projection stage. Another tube leads from 

 the cooling chamber to a vessel on the floor at a lower level than the 

 trough. A gentle sucking at this second tube will start the siphon, and 

 the flow of the liquid can be controlled by a pinchcock. A difference of 

 level equal to 50 or 60 cm. is found to be sufficient. It is easy to see 

 that there is now no risk of damage to the cover-glass. By exchanging 

 the levels of trough and vessel and adjusting tube-lengths the flow can 

 be reversed and the same liquid used again. 



* Joum. Quekett Micr. Club, xii. (1914) pp. 301-8 (3 pis.), 

 t Zeitschr. wiss. Mikrosk., xxxi. (1914) pp. 99-100 (2 figs.). 

 % Zeitschr. wiss. Mikrosk., xxxi. (1914) pp. 97-8. 



