ZOOLOGY AND BOTANY, MIOROSOOPY, ETO. 



1033 



The nearer the objects to be pbotograpbed are to the focusing disc, 

 the greater distance must the lenses of the eye-piece be removed from 

 one another. On the whole the lengthening varies from 1 to 2 cm. 



Illumiiiatioii of Objects in Photomicrography.*— Dr. M. Stenglein 

 gives the results of his experiments on this subject. In photographing 

 a microscopical preparation, .the light is passed through a condensing 

 lens on to the object, the image of which is thrown on some white screen. 

 If now the object be removed, the image of the light will appear in its 

 place. And the examination of this picture shows that its surface is not 

 illuminated with perfect regularity, but that all the irregularities of the 

 zirconium and calcium plates are reproduced in the zirconium and 

 calcium lights. If a petroleum lamp with circular wick be used, the 

 dark streak in the centre of the flame appears. 



If now the image of the light be made to approach the objective, it 

 will be noticed that the above-mentioned image gradually disappears and 

 in its place there appears upon the white disc a circle which is more or 

 less bright, according as the position of the image is in the objective or 

 in front of it. 



Now if the illuminating lens be covered with a screen behind which 

 in a properly darkened room the cone of light can be observed, it will 

 be rendered evident that when the greatest possible brightness of the 

 light-circle is observed on the white screen, the cone of light is inter- 

 rupted at the aperture of the objective. 



If the cone be smaller than the objective's aperture, the image of the 

 light shows more or less sharply on the white screen, and therefore all 

 the shadow-lines of the source of light. If the cone be larger than the 

 aperture, then the light and dark circles appear. If, having in the above 

 described way obtained the greatest brightness and a regular illumina- 

 tion, the object to be photographed is inserted, it will be found that the 

 sharpness of the image towards the margin is much increased. 



The author's experiments were made with Klonne and Miiller's 

 1, 2, 3,4 objectives, and an apochromatic of Zeiss with 0*30 aperture 

 and 30 • mm. focal distance. 



Zirconium Light for Photomicrography.! — Herren Schmidt and 

 Haensch have recently brought out a new burner for photomicrographic 

 purposes ; in this zirconium replaces the calcium cylinder, which is found 

 in practice to become partially consumed, and hence a rapid deteriora- 

 tion of the light. Zirconium is found to be very resistant, even in the 

 hottest part of the flame, and a small plate thereof fixed in platinum and 

 placed in the hottest part of the flame gives a splendid white light, the 

 spectrum of which extends from A to H, and is perfectly continuous, 

 being unbroken by any lines. The advantages of the light are that it 

 gives a regular flame in any position, and when focused for the optical 

 axis of an apparatus the illuminating point remains steady at the same 

 spot. 



Arsonval, — d'. — Nouvelle Itimiere par incandescence du gaz d'eclairage. Appli- 

 cation a Texamen niicroscopic[ue, a I'analyse spectrale et la photographie. (New 

 incandescent gas-light; its application to microscopical examination, spectral 

 analysis and photography.) CR. Soc. Biol, V. (1888) No. 8. 



* Centralbl. f. Bakteriol. u. Parasitenk., iii. (1888) pp. 511-2. 

 t Zeitschr. f. Wiss. Mikr., v. (1888) p. 225. 



