﻿72 Scientific Intelligence. 



dacyte are often quarizophyric ; in addition to true augite rocks, 

 trachyte, andesite, etc., are sometimes augitophyric ; different 

 diabases or dolerytes and basalts are labradnphyric, anortho- 

 phyric, augitophyric or chrysophyric ; and the same specimen is 

 often both augitophyric and chrysophyric, and sometimes also 

 labradophyric. In a similar way sphcerophyric may be applied 

 to a crystalline rock containing spherulites or concretions of 

 any kind, distinguishing the structure, thus, from concretionary 

 by concentric deposition, or that common in uncrystalline 

 rocks. 



This list of adjectives can be extended if precision in the 

 description of rocks requires it. 



SCIENTIFIC INTELLIGENCE. 



I. Physics and Chemistry. 



1. On a new Absolute Electrometer. — Bichat and Blokdlot 

 have presented to the French Academy a new absolute electrom- 

 eter, based on the attraction of two concentric cylinders, which 

 is easy to construct and which gives continuous indications. An 

 insulated hollow cylinder of metal is connected to the point whose 

 potential is to be measured. A second cylinder is suspended, con- 

 centrically within the first, from the arm of a balance, which, is 

 connected to the ground. A third cylinder slightly larger than 

 the second, encloses its lower third and projects considerably be- 

 low the first and outer cylinder. This cylinder, as well as a metal- 

 lic screen between the cylinders and the balance beam, is con- 

 nected to earth. The first or outer cylinder exerts upon the 

 second or suspended cylinder an attraction upward. These two 

 constitute a condenser, the length of the former in relation to the 

 latter being such that in the middle section the equipotential sur- 

 faces between them are concentric cylinders and the lines of force 

 radii; while above and below this the distribution varies. If 

 now the suspended cylinder rises above the enclosing third cylin- 

 der by a small amount, the change in distribution may be con- 

 sidered to consist of a simple elongation of the uniform portion, 

 the superior portion where the distribution is irregular being 

 simply displaced. If F be the upward force on the suspended 

 cylinder and clz its displacement, the work done by the electric 

 forces is Fdz. But this work is equal to the increase of the energy 

 of the system; and this is proportional to -J-QV", in which Q rep- 

 resents the increase of charge and V the potential of the outer 

 cylinder. But Q=CV, the product of the capacity of a portion 

 of the cylindrical condenser of height dz by the potential ; and 



dz 

 this capacity is equal to R , in which R and r are the radii 



° g 7~ 



