202 Miscellaneous Intelligence, 



802°, polarity is not manifested until the temperature has fallen 

 2 or 3 degrees. In all these cases, it remains to the end of the 

 cooling ; but if at any time the temperature of the air about the 

 glass tube is raised 2 or 3 degrees, polarity disappears. These 

 effects are analogous to those produced by the tourmaline under 

 the same circumstances of heat, except that in the glass they are 

 determined by the excited electric, and in the tourmaline by the 

 peculiarities of crystallization. 



A small cylinder of gum-lac used in place of the glass tube was 

 rapidly attracted by the excited electric at the moment of cooling 

 from 68° or 77° ; but the polar state was very difficult to produce, 

 and continued for a very short time. 



In these experiments the excited electric should have a nearly 

 constant state ; one of the poles of a dry pile answers the purpose 

 very well. 



M. Becquerel considers the theory of M. Ampere as accounting 

 for some of these effects very well, but not for the permanency of 

 the poles during cooling. The theory supposes atoms to have an 

 electricity which is proper to them ; which, acting as neighbouring 

 bodies, decomposes their natural electricity or electricities, attracting 

 that of a different name, and repelling that of the same name, as in 

 the Leyden bottle ; then these atoms become surrounded by an 

 electric atmosphere, which partly hides the electricity proper to 

 each, &c. 



M. Becquerel finds that the electric effects of tourmalines vary 

 with their length, and he concludes, doubtless, with their breadth ; 

 so that the intensity of the electricity developed may well be con- 

 sidered as a function of these two quantities. Small tourmalines 

 become more highly and readily electric than large ones. Large 

 tourmalines which could not be electrized by heat alone, when 

 broken gave fragments readily rendered electric. Admitting that 

 this law is applicable, however much the size is reduced, it results 

 that the integral molecule, should acquire an intense electric polarity 

 for very feeble variations of temperature. 



Some facts induce M. Becquerel to suppose that the colouring 

 matter of tourmalines may modify their electric properties. — Ajin. 

 de Chimie, xxxvii. 369. 



6. Electro-magnetic Current from heated Fluids. — M. Nobili 

 connects the two ends of his galvanometer wire with the saline 

 solution in two cups, and then these cups with two others contain- 

 ing more of the same solution, by bundles of moistened cotton. 

 Two small cylinders of clay are then made, and, when necessary, 

 connected with the cups by moistened cotton, so as to constitute the 

 ends of the arrangement. When one of these cylinders is dried, 

 then strongly heated, and suddenly thrust two or three inches deep 

 into the other soft and moist cylinder, the needle of the galvano- 

 meter deviates as much as 80° from its natural position. This 



