ij84 Mimalayah Mountums-. 



Mr. Phiquepal, whom I mentioned in my former letters^ 

 is no doubt by this time on your side of the Atlantic. I have 

 already informed you that he carried with him forty or fifty 

 large cases of prints, instruments, and books, necessary for 

 the elucidation of the sj/stem which he teaches. The most 

 important object is to give, first, a correct knowledge of sub- 

 stances, and afterwards words or signs. As he is intimately 

 acquainted with the properties of matter, there is every rea- 

 son to expect success ; and I hope his example will be fol- 

 lowed by other schools, so far at least as to give to children 

 ideas of things by their exact representations, instead of the 

 vague and undefined method in common use. 



21. Optical Structure of Minerals. — The optical structure 

 of minerals it is well known has thrown much light upon their 

 composition. Dr. Brewster has lately examined a specimen 

 of the lithionmica of Prof. Gmelin, and has ascertained that 

 these plates are composed of crystals with one axis, united 

 to crystals with two axes. Now as all the uniaxal crystals of 

 mica yet examined differ in chemical composition from the 

 biaxal ones, Dr. Brewster recommends Prof, Gmelin to de- 

 tach all the uniaxal parts if possible from the biaxal parts, and 

 to make a separate analysis of both. If he finds what analo- 

 gy authorizes us to expect, that these two portions are chemi- 

 cally different, the result will be a most important one, both 

 for mineralogy and analytical chemistry. It will set aside all 

 analyses of minerals, where it is likely that the body analysed 

 has not been an individual crystal, and it may thus establish 

 upon a firmer basis the law of definite proportions. 



22. Hirnalayah Mountains.'^ — Upwards of 25,749 feet have 

 been stated by two eminent mathematicians, Captains Hodg- 

 son and Herbert, as the elevation, trigonometrieally ascertain- 

 ed, of one of the Jowahir peaks. Calculations have been usu- 

 ally founded either upon comparison with the medium height 

 of the barometer in Calcutta, or at the level of the sea (per- 

 haps 1200 miles off) during the month in which the observa- 

 lion on the mountain was made. Even where contempora- 

 neous observations are obtained, have we ascertained that 



* Extracted from a paper by George Govan, M. D. in Dr. Brewster's 

 F-(iin. Jour, of Science, Vol. II. 



