Miscellanies. 379 



light, and taking the most favorable point ; thus, for example, it af- 

 fords the degree of light most advantageous for seeing at the same 

 time the borders of the sun and the threads of the micrometer which 

 are not yet on his disk, — an advantage not always had with uniform 

 dark glasses, in variable states of the atmosphere, unless we have a 

 great number of them, and even then much valuable time must be lost 

 in the adjustment of them to the instrument. — Bib. Univ. Nov. 1832. 



2. Optical properties of saccharine juices. — M. Biot read, on 

 the 10th of December, a memoir on an optical character by which 

 those vegetable juices which produce sugar analogous to that of the 

 sugar cane, may be immediately distinguished from those which only 

 yield sugar similar to that of grapes. 



This character consist in the direction in which a polarized ray is 

 turned, on the one hand, by the juice of grapes, pears, apples, goose- 

 berries, and other fruits which furnish sugar that will not crystallize ; 

 and on the other, by the juice of cane, beets, parsnips, turnips, car- 

 rots, he. Liquids of the first class, turn the light to the left in every 

 degree of concentration, until solidification takes place. It is at this 

 point only that by a sudden change they may turn it to the right- 

 Juices of the second class, on the contrary, always give it the latter 

 direction. The phenomena observed by M. Biot in the juice of 

 beets, induce him to think that ten per cent, of sugar may be obtain- 

 ed from it, as M. Pelouze has already stated. He thinks also that 

 it would be advantageous to cultivate parsnips to a greater extent, 

 which, on account of the great quantity of sugar they contain, would 

 make excellent food for cattle. He has observed certain characters 

 which, he thinks, may serve, in a general point of view, to determine 

 whether a substance, obtained by a chemical operation, existed prior 

 to that operation, or whether it results from it. Finally, the sudden 

 changes which he has remarked in the direction, by solidification, 

 induce him to refer these phenomena, to molecular and dissymmet- 

 rical forces. — Idem. 



3. New air pump. — M. Thilokier has invented an air pump,, 

 without any valves or stop cocks to interrupt or complicate its action. 

 The air of the receiver passes into a Torricellian vacuum, and by 

 the motion of the machine, the Torricellian tube is reversed — the air 

 escapes into the atmosphere, — a new vacuum is formed into which 

 an additional portion of air passes from the receiver, and so on until 



