236 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



microscopy ; they furnish no trace of detail and present an appearance 

 of briglit point-like disks, generally surrounded by bright and dark 

 rings. 



Half-shadow Interferometer as Photometer.* — C. Zakrzewski 

 draws attention to recent methods for increasing the accuracy of 

 measurements of phase difference by the interferometer. The principle 

 of the measurement depends not so much on the displacement of the 

 interference fringes as on the introduction of a half-shadow. The type 

 of instrument used is therefore called a half-shadow interferometer. 

 The author points out that without much difficulty it can also be 

 applied to photometry. 



Kriiss Universal Arc Lamp, with steady Light-source.t — This 



apparatus (fig. Si) consists essentially of a lamp-chamber with carbons 



Fig. 34. 



mutually perpendicular. This arrangement secures a steady light-source, 

 the approximation of the carbons in the required proportion being effected 

 by the lateral handwheel. The light-diffusing crater of the horizontal 

 positive carbon therefore always remains in the optical axis of the small 

 condenser lens. The carbons lie on two insulated rollers, and are urged 



* Bull. Int. Acad, cles Sci. Cracovie, Classe Sci. Math., 8a (1911) pp. 545-7 (1 fig.) 

 t Zeitschr. f. Pliys. u. Chem. Unterr., xxiv. (1911) p. 283. See also Deutsche 

 Mech.-Zeit., xxiii. (1911) p. 241. 



