374 Miscellanies. 



(among other substances,) finely divided Platinum sponge, Antimony, 

 Potassa, Lime, Silica, Carbonate of Lime, he. These actions are, 

 as was to be expected, aided by an elevation of temperature above 

 60° F. 



These results I am led to believe from a partial trial, will find use- 

 ful application in Eudiometry by means of Phosphorus. 



12. On the use of black mica, as a substitute for colored glasses in 

 spectacles; by Dr. William Meade, in a letter to the Editor, dated 

 Newburgh, March 19, 1830. 



Dear Sir — ^While my eyes were weak, during the last winter, I 

 suffered great inconvenience in consequence of the glare of the snow 

 on the mountains and the river, and I found a substitute for glass 

 spectacles which answered beyond my expectations, and gave me 

 the greatest relief. It is far better than green glass ; it gives a most 

 agreeable sombre light and is peculiarly pleasant for tender eyes; 

 not however to read with, but merely to defend the eyes from the 

 influence of the light of the sun or snow. As 1 find it equally use- 

 ful and agreeable at candle light or when looking at a fire, it occurred 

 to me that great convenience would be attached to the use of spec- 

 tacles in which these shades may be inserted instead of glass, when 

 making chemical or galvanic experiments, particularly when the large 

 galvanic apparatus is used, which produces such intense light that 

 few eyes can bear it. On these occasions I have always seen Dr. 

 Hare wear glasses; but these are Hable to several objections. First, 

 great danger attends breaking; they also are distressing when they 

 get warm, and the glare is never so effectually counteracted as in the 

 black mica which I send you, and which may be made of any shade 

 most agreeable to the sight in proportion to the thickness of the lami- 

 na; nor will this mica become heated and disagreeable to the eyes 

 in the summer. 1 have now had several weeks' trial of them and am 

 quite satisfied with their superiority over glass. I have given them 

 to others, who also acknowledge their superiority, particularly a young 

 lady who lives near me, and who has such tender eyes that she never 

 can venture out without colored spectacles, but from the moment she 

 has adopted my plan she has found such benefit that she has quite 

 given up the green glasses. 



I have enclosed you in this letter two or three thin plates of this 

 black mica, which I have never found any where but in the town of 

 Munro, in the state of New York, but it is now rare ; it is found crys- 



