238 SUMMARY OF CURRENT RESEARCHES RELATING TO 



dered impossible. The stand is arranged so that the lamp can be easily 

 turned and rotated in every direction, tlie small size of the lamp very 

 much aiding the facility of such movement. The lamp burns best with 

 a current-strength of 4 amperes ; it can be adapted to any installation 

 of 65, 110 or 220 volts, with the insertion of a suitable resistance. It 

 can be supplied for direct or for alternating currents. 



The lamp is suitable for optical demonstrations, microscopical work, 

 micro-projection, and diapositive projection. Fig. 35 shows the applica- 

 tion of the lamp to the purposes of microscopic objects with an ordinary 

 microscope stand. In fig. o6 the apparatus is fitted up for diapositive 

 projection. Both figures will be easily understood. 



Radiant Efficiency of Arc Lamps.*— H. P. Gage undertook an 

 investigation for the purpose of determining the radiant efficiency and 

 the mechanical equivalent of the light from the right-angle carbon arc 

 and the Bremer flaming arcs. His experiments led to the conclusion 

 that the A line, 0'76yu., is not a suitable point to take for the limit 

 of the visible spectrum. An examination of luminosity curves showed 

 that it w^ould be preferable to assume this limit to be at 0'68/a, and 

 that if all radiation of greater wave-length than 0'68/a were removed 

 the resulting decrease in light could be neglected. A modification of 

 Angstrom's method was used, and the greatest efficiency was found in 

 the arc stream between yellow flame carbons, the carbon tips being 

 shaded. AVith this arc the light energy constitutes 39 p.c. of the energy 

 radiated. 



Orueta y Duarte, Domingo de — Nota sobre la nueva lampara electrica 

 Nernst, para microfotografia y proyecci6n, del Dr. A. Kohler, con algunas con- 

 sideraciones sobre el alambrado del microscopio. 



Boll, de la Real Sociedad espatlola de Historia natural 

 (October, 1911) pp. 397-406 (1 fig.). 



C4) Photomicrography. 



Cinematography of the Embryonic Development of the Sea-urchin. f 

 The details of the apparatus used for the above purpose Ijy L. Chevroton 

 and F. Yles are essentially those described under the title Chrono- 

 photography in this Journal. § The light-source is an adjustable voltaic 

 arc of 20 to 50 amperes of continuous current. This light-source is 

 adjusted on an optical bench in axial alignment with condensers, water- 

 chamber, sector-disk, absorption-screen, and iris-diaphragm. The beam 

 of light, after traversing the above, impinges on the mirror of the Micro- 

 scope and is reflected upwards (the Microscope being vertical), through 

 chronophotographic apparatus, into the camera. By means of a tele- 

 scope-tube the stand and chronophotographic apparatus are brought into 

 intimate connexion, and loss of light prevented ; this is considered to be 

 an essential condition. The Microscope ocular is either dispensed with, 



* Physical Kev., ii. (1911) pp. 111-27 (12 figs.). 



t Arch. Zool. Exp6r. et G6n., ser. 5, viii. (Paris, 1911) pp. 499-517 (6 pis. and 

 5 figs.). § See this Journal, 1909, p. 648. 



