On the Optical Properties of Chrysammate of Potash. 171 



Sweden accounted for on any known principles of slow accu- 

 mulation ? and can the drift whicli is so extensively spread over 

 central and northern Europe be considered solely as the drop- 

 pings of icebergs ? " Verily/' as it has been wittily said, " palaces 

 are not built with a teaspoon, nor hospitals endowed with a pinch 

 of snuff!" 



Pulborough, Feb. 13, 1854. 



XXV. On the Date of the Discovery of the Optical Properties of 

 Chrysammate of Potash. In a Letter from Sir David Brewster 

 to Professor Stokes*. 



My dear Mr. Stokes, 



PROFESSOR FISCHER has put into my hands this after- 

 noon a copy of your interesting paper " On the Metalhc 

 Reflexion exhibited by certain Non-metallic Bodies," in which I 

 observe the following passage : — 



" In mentioning my own observations on safflower-red, Hera- 

 pathite, &c., nothing is further from my wish than to neglect the 

 priority of those to whom priority belongs. M. Haidiuger had 

 several years before discovered the phsenomenon of the reflexion 

 of differently coloured oppositely polarized pencils, which Sir 

 David Brewster shortly afterwards, and independently, discovered 

 in the case of chrysammate of potash." 



jNIy experiments were made in the end of 1842 and the begin- 

 ning of 1 843, with crystals of chrysammate of potash sent to me 

 on the 2nd of December 1842 by J\Ir. Schunck, along with 

 other seven new substances, aloetinate of potash, &c. Mr. Schunck 

 directed my attention to the gy-een metallic lustre of the salt, and 

 to the redness of its solution, which I instantly examined. 



I found it very difficult to work with such imperfect crystals, 

 and I delayed publishing the imperfect results which I had 

 obtained in the expectation of some time or other getting better 

 crystals. 



On the 1st of March, 1846, I read to the Literary and Philo- 

 sophical Society of St. Andi-ew's all the observations inserted in 

 my journal of experiments ; and not being able to attend the 

 Southampton ineeting of the British Association, I made an 

 abstract of what I had read at St. Andrew's, which is the paper 

 you refer to as published in the Report of the Association. 



In 1842 and 184.3 I examined also various other substances, 

 but 1 have not published any of the results which I obtained. 



I enclose Mr. Schunck's letter, which will show you that I 



* Communicated by Professor Stokes. 



N2 



