Dr. Woods on a New Actinometer. 39 
the metamorphosis of these minerals in granite, the author en- 
deavoured to heat them in closed glass tubes full of air, the 
expansion of the air by the heat giving rise in this case to a con- 
siderable pressure. He proved that incandescence took place 
quite as well in this case—in fact, that it was even facilitated by 
pressure. . 
One might, it is true, suppose that these minerals, especially 
Gadolinite, were formed at the same time as the granite and by 
fusion, but that afterwards, under the prolonged influence of 
the atmosphere, water, an elevated temperature and perhaps 
other causes, they had undergone a metamorphosis accompanied 
by a fixation of caloric, and that thus they had passed into another, 
isomeric state in which they are capable of disengaging their 
latent heat by calcination and of presenting the phenomenon of 
incandescence. 
Prof. Rose observes that this hypothesis contains nothing con- 
trary to the views which he advances. Certainly no one imagines 
that the elements of granite have been in a complete state of 
aqueous solution, from which, by degrees, they have been sepa- 
rated by crystallization. It is possible that these elements 
proceed from an anterior rock which had an igneous origin, 
and which had assumed the crystalline state under the in- 
fluence of water, heat, and pressure, as in the experiments by 
which M. Daubrée succeeded in obtaining several crystallized 
minerals. A similar hypothesis has often been published, par- 
ticularly by Mr. Sterry Hunt. It has the advantage of explain- 
ing the absence of organic remains in granite, although this rock 
might have been formed after the appearance of organized beings. 
It is clear that these observations apply, not only to granites, 
but to all crystalline rocks containing quartz, especially to 
quartzose porphyries and trachytes. The hypothesis of the 
igneous origin of these rocks is incompatible with the actual 
state of our chemical knowledge. 
VIL. Description of a new Actinometer, 
By Tuomas Woops, M.D.* 
Lo edhe DRAPER, of New York, published a paper in 
this Magazine for September 1857, in which he showed that 
a solution of peroxalate of iron is decomposed by light, protox- 
alate of iron being formed with evolution of carbonic acid— 
Fe? 08, 3C?0?= 2FeO, C?0? + 2C0?. 
In order to find the amount of actinism which had caused the 
change, the quantity of protoxalate produced, or of the carbonic 
* Communicated by the Author. 
