486 SUMMAEY OF CUERENT KESEARCHES RELATING TO 



4 volts, and is screwed into the holder. A dry battery is supplied, 

 which with intermittent use may last for more than 6 months. The 

 apparatus can be fitted with 8- and 12-volt lamps for use with various 

 accumulators, and even with the ordinary house current by means of 

 special adapters. The apparatus is made by F. Davidson and Co. 



Heimstadt, 0. — Spiegelkondensor fiir ultramikroskopischeBeobachtungen. 



Zeitschr. f. Chem. u. Ind. d. Kolldide, 

 Jahrg. 1, 1907, heft 9. 



(4) Photomicrography. 



Instantaneous Photomicrography.* — C. A. Fran9ois-Franck gave a 

 demonstration of the results he obtained by means of instantaneous 

 photomicrography and of chronophotomicrograpliy. The objects were 

 taken under magnifiaition varying from 60-600 diameters, and included 

 the movements of the appendices, of the heart and intestines of 

 Daphnia, colonies of VorticeUa, respiratory appendages of the larvas of 

 Epiwnera, branchia of Arenicola, etc. 



Leitz, E. — Neuer mikrophotographische TTniversalapparat. 



Zeitschr. f. wiss. Mikrosk., xxiv. (1907) p. 40. 



LowENSTEiN, E. — Versuche iiber Dreifarbenmikroskopie. 



Zeitschr. f. Tubcrk, x. (1906) p. 34. 



(5) Microscopical Optics and Manipulation. 



On the Nature of Optical Imag-es.j — Albert B. Porter draws 

 attention to the want of general recognition that all optical images arise 



\i 



1 zsz^ CZJ ^ 



Fig. 82. 



by interference, and are, indeed, particular cases of interference patterns, 

 and describes a simple experiment which shows the relation between 

 interference and image formation in a striking manner (fig. 82). 



The experiment consists in passing a parallel beam of monochro- 

 matic light through a coarsely ruled, black-line, diffraction grating, and 

 then through a convex lens. On the far side of the lens a system of 

 sharply defined interference fringes isformed which can be seen by aid of 

 an eye-piece, or intercepted on a screen, at any point over a considerable 

 range along the axis. Somewhere in this system of fringes is the 

 geometrical image of the grating, but it is visually quite indistinguish- 



* C.R. See. Biol. Paris, Ixii. (1907) pp. 964-7. 

 t Physical Review, xxiv. (1907) pp. 303-6 (1 fig.). 



