2/0 i^ew OuUines of Chemical Philosophy, 



the mica, I observed the image to vanish in the direction M7» 

 and Vp, which I considered as obHque neutral axes ; but I have 

 since found that this was owing to the polarization of the pencil 

 by oblique transmission, a property of light which I had not then 

 discovered. 



We have hitherto considered the depolarization of light as 

 effected by two separate bodies, one of which polarizes the in- 

 cident rays, while the other deprives them of the polarity which 

 they have thus acquired ; but in all bodies that possess oblique 

 depolarizing axes, light may be polarized and depolarized by 

 the same crystal. Thus if ABo^, Plate IV., fig. 7, be a plate of 

 topaz having DE for its oblique depolarizing axis, and if a ray 

 RR' of common light is incident at R' with such an obliquity 

 that it is polarized by being reflected at C from the posterior 

 surface ah, then the ray rr' will be depolarized in its passage 

 from C to r along the oblique axis of depolarization, and the 

 emergent ray rr' will be depolarized light. Hence it follows 

 that the angle TiCh, which the oblique depolarizing axis makes 

 with the posterior surface ah, is nearly equal to the comple- 

 ment of the angle OCr, at which light is polarized by reflection 

 atC*. 



[To be continued.] 



XLIII. New Outlines of Chemical Philosophy. By Ez. Walker, 



E^^. of Lymi, Norfolk. 



[Continued from p. 350, vol. xliii.] 



J. HE causes from whence arise all those various phenomena of 

 our atmosphere, commonly called ni,eteors, have never been in- 

 vestigated in a satisfactory manner. It is probable, however, 

 that they are the effects of some universal cause. It is already 



* Since tlie precediDg section was written, I have performed a very ex- 

 tensive series of experiments on the depolarization of light, and have thus 

 teen led to a satisfactory generalization of the pha^nomena. In this theory 

 the phaenoinena are referred to the general principle of polarization : such 

 ■bodies as have neutral and depolarizing axes are supposed to form two 

 images polarized in an opposite manner, and either produced by the same 

 or by different refractive powers; vsliile those which depolarize light in 

 every direction, like gum arable, caoutchouc, &c. are composed of films or 

 lavers, each of which is a doubly polarizing crystal, (he neutral and tlie 

 depolarizing axes of one film not being coincident with the neutral and de- 

 polarizing axes of the rest. In a sc^parate memoir, which I have drawn up^ 

 for the consideration of the Royal Society, I have given a full account of 

 this theory, of the experiments on which it is founded, and of the nevr 

 »iews to which it leads respecting the ftjrmatioo and structure of organized 

 teatter. 



knowii 



