240 



SUMMAUV OF CURRENT RESEARCHES RELATING TO 



the best daylight. The apparatus, which takes up little space and is 

 easily arranged, is made by E. Leitz. 



Fig. 50. 



Foucault's Heliostat.* — In this instrument (fig. 51), which can be 

 adapted to different latitudes, the mirror has a diameter of 30 cm. 



Fig. 51. 



* Catalogue (1907) of the Soc. genevoise pour la construction d' instruments de 

 physique et de rnecanique, pp. 87-8. 



