APPENDIX. 



No. 1. 



On the Optical Phenomena of certain Crystals. 

 BY H. F. TALBOT, ESQ. F.R.S.* 



SOME time ago I had the honour to communicate to the 

 Royal Society an account of my invention of the pola- 

 rizing microscope. This instrument possesses so great 

 a power of developing the internal structure of trans- 

 parent bodies, even in their minutest visible particles, 

 that I feel confident the employment of it will lead to 

 many new and interesting results. At present I mean 

 to confine myself to the description of a phenomenon 

 which shews strikingly the beautiful order and regula- 

 rity with which nature disposes the fabric of some of her 

 minutest visible works. 



The object I speak of is a kind of minute crystalliza- 

 tion which may be obtained in peculiar circumstances, 

 and I doubt not in many different ways ; but the manner 

 in which it has presented itself to my observation is as 

 follows : 



A crystal of borax is placed in a drop of phosphoric 



* From Phil. Trans. Part I. for 137. 



