On the origin of Feldspars. 435 
magnetic apparatus and his induction machine. The last machine, with 
two of Bunsen’s pairs, affords, in the air, sparks about two centimeters 
(nearly eight inches) Jong, and in a vacuum, waves of light comparable — 
to those of a powerful electric machine, although having many distinguish- 
ing characteristics, By a recent improvement, Mr. Ruhmkorff has greatly 
increased its power; and with 25 of Bunsen’s pairs, he produces sparks 
80 centimetres long; and for certain effects it is superior to a friction 
battery. 
_ Prize in Geology.—This prize, the subject of ‘which is The Metamorph- 
ism of rocks, has not been awarded. ‘The Academy continues the sub- 
Ject, under the following terms. The authors should review the history 
e 
of all attempts, since the close of the Jast century, to explain, on th 
rocks, They should review the physical and chemical theories proposed, 
Academy would have tlem 
mention the experiments they have made to verify and extend the theory 
of metamorphic phenomena. The prize is a medal of gold, of 3000 francs, 
Another prize of the same value will be awarded on the following ques- 
tion—* To determine experimentally what influence insects may exert on 
the diseases of plants ;” and another on the subject “ The mode of fecun- 
dation of eggs and the structure of organs of generation in the principal 
natural groups of Polyps and Acalephs.” (To be concluded.) 
still preserved. 
While arranging an apparatus in which I proposed to heat pe 
Pressure a solution of carbonate of potash y oe 
hope of obtaining a double silicate of alumina and potash, Mr. Daubrée 
announced to the French Academy of Sciences (Comptes Rendus, » sh 
16, 1857) that he had succeeded in obtaining erystalline feldspar, mixed 
With crystals of quartz, by heating during a month, a mixture of kaolin 
and silicate of potash to 400° C. He has moreover shown that feld-pars 
pyroxenes are very stable in presence of heated alkaline solutions, 
and that crystallized diopside and wollastonite are formed when artificial 
* See this Journal, vol. xxv, p. 287, also vol. xxiii, p. 437. 
