236 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



compensator in genera] view and in sect inn. Xo description is furnished 

 with the illustration. 



• 



Fig. 44. 



Fig. 45. 



Fig. 46. 



C3) Illuminating- and other Apparatus. 



Pearce's Total Reflexion Refractometer.* — This instrument (fig. 

 •47), numbered 2190 in the catalogue of the Genevan firm, has been 

 made after the designs of F. Pearce. The general view recalls that of 

 Abbe's refractometer, but Pearce's optical arrangements are suitable for 

 measurements upon large as well as upon small fragments. In case of 

 large fragments, an objective 0' and an ocular A' replace the objective 



* Soc. genevoise pour la construction d'instruments de physique et de rne- 

 canique, Special circular, 1907. 



