IS 14.] Scientific JnteUigence. 311 



By applying high magnifying powers, I discovered that motlier-of- 

 pearl had an elementary grooved structure like the delicate texture 

 of the skin of an infant's fingers, and that the dlrectwn nf the 

 groove: is always perpendicular io the axis of extraordinary reflec- 

 tion. In some pieces of raother-of-pearl these grooves can be seen 

 with a power of 8 or 10 times. In other pieces it requires a power 

 of 400 to see them : and in some pieces they cannot be detected by 

 any power which I have been able to apply. In irregularly formed 

 motiier-of-pearl the grooves are arranged circularly, like the veins 

 in the hammered agate, and exhibit a number of very curious 

 appearances. The same grooves are seen on the surface of the wax 

 and metals after tliey have been impressed with the mother-of-pearl. 

 These experiments lead to a number of important optical conclu- 

 sions, which could scarcely be understood in a brief notice like the 

 present ; and they prove incontrovertibly that there exist near the 

 surface of bodies new forces which act upon light, and which are 

 totally different from the ordinary forces which produce refraction 

 and reflection. 



III. On a New Method of Polarizing Light peculiar io Mother-qf- 



Pcarl 



This substance possesses the singular property of polarizing light 

 in a way different from all bodies, whether crystallized or uncrystal- 

 lized. In all doubly-refracting crystals the opposite polarization of 

 the two images is always related to some axis or fixed line in the 

 primitive form; while in all uncrystallized bodies, such as a bundle 

 of plates of glass, or a bundle of films of gold-beater's skin, the 

 polarisation is related to the planes of reflection and refraction, the 

 reflected pencil being always polarised in an orposixE manner to 

 the refracted pencil, like the two images formed by calcareous spar. 

 In mother-of-pearl, however, a single plate possesses the property 

 of polarizing the ivhole of the transjnitted light at an angle oj' inci- 

 dence of GOi° ; and what is still more extraordinaiy, the transmitted 

 pencil is polarized in the same manner as the reflected pencil. By 

 turning the plate of mother-of-pearl about its centre so as to pre- 

 serve the same inclination to the incident ray, no change wiiatever 

 takes place. Mother-of-pearl also polarizes light, and exhibits the 

 coloured rings which are described in the Annals of Philosop/wy 



JyJ^ XV. p. i;*3. 



IV. Salt sulUmed during the Inirning of Bricks. 



I received some weeks ago from Mr. Trimmer a sjjccimen of a 

 salt which, he informed me, made its appearance on the top of biic k- 

 l:ilns during the burning of bricks, 'i his salt, 1 find, has tlie 

 following properties : — I. It is in powder or in small lumps, and 

 has a white colour. '2. Its taste is saline and cooling, precisely the 

 same with the taste of sal ammoniac. :). When heated it docs not 

 melt, but sublimes completely in a white smoke, whicli has the 

 \vcll-kno«n imcll of sul ammoniac, and may be condensed by 



