NOTES FROM THE SOCIETY S NOTE-BOOKS. 



117 



POLARISCOPIC. 



Polarised Light— The beauty of polarised objects causes the 

 very frequent enquiry — "What is Polarised Light?" I cannot 

 think of a better explanation than that given by stating that all 

 beams of light are systems of waves vibrating in different planes. 

 The polariser arranges these beams of light in sets ; say in hori- 

 zontal and perpendicular sets. And then each of these sets is 

 absorbed or cut off by the subsequent crystals, if turned at right 

 angles. This will be understood by the annexed Figure. 



Fig. 2 2. 



The gridiron a stops the horizontally disposed rays (or vibrations 

 of rays) ; the gridiron b would allow the perpendicular vibrations 

 to pass, if it were placed the other way up (if x were where y is) ; 

 but having been revolved till it crosses the gridiron a at right 

 angles, all vibrations are stopped. 



It may interest those who use selenite to know that this was 

 the material used by Tiberias Caesar for glazing his greenhouse. 



C. P. Coombs. 



BOTANICAL. 



Fig Tree, tr. sec. of a young shoot— In this section crystals 

 may be seen near the outer edge, but they are better shown in a 

 longitudinal section ; they appear to be somewhat cuboidal or 

 lozenge shaped. I do not think they are Sphaeraphides, although 

 Dr. GulUver mentions such as being found in the Ficus. 



. A. COWEN. 



