302 Captain Lachlan's Observations on the 



chanically included between the lamellae ; proving that it is 

 essentially the same mixture which forms both species, whose 

 difference merely depends on the arrangement of their parti- 

 cles. Hence, Mitscherlich infers, that a movement of the 

 particles within a solid body may take place, by which they 

 are otherwise symmetrically arranged, and form a new spe- 

 cies, which, in the above mentioned salts, alone exists above a 

 temperature of 42° R. (126° Fahr.) Did our temperature never 

 go below that, we would not know the ordinary prismatic salts 

 at all, or, at least, they would be as difficultly obtained, as the 

 six-sided low prisms of hydrous chloride of sodium, which but 

 few chemists have had occasion to observe. After the change, 

 no more cleavage is visible, and though the compound mass 

 of crystals is yet coherent, it yields to a gentle pressure, and 

 crumbles into pieces. Changes produced in a somewhat ana- 

 logous manner, have been observed in several dimorphous bo- 

 dies. According to Mitscherlich, the sulphur obtained by 

 fusion in hemi-prismatic crystals, is quite transparent, but 

 after a day or two it becomes opaque. It is well known, that 

 Arragonite, when exposed to a higher temperature, will at 

 once fly into powder, while calcareous spar, heated along 

 with it side by side, remains unchanged, and even retains its 

 transparency. It is highly probable, that, in the first in- 

 stance, prismatic sulphur, in the second, rhombohedral lime- 

 haloide are formed. 



Berlin, February 12th 1826. 



Art. XXIII. — Observations on the Geography of the Bur- 

 rampooter and the Sanpoo Rivers. By Captain R. Lachlan, 

 17th Regiment. In a Letter to the Editor. 



My Dear Sir, 

 Accept of my best thanks for the perusal of the Sketch Map 

 and printed Extract, descriptive of Lieutenant Burlton's Re- 

 searches in Assam, regarding the source of the Burrampooter, 

 which I return herewith.* Knowing as you do, that, in conse- 



* This Lithographic Map, for which I have heen indebted to an esteem- 

 ed correspondent in India, is entitled, " Sketch of the Country bordering 



