198 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ductivity is parallel to the intersections of the planes of most 

 easy cleavage, and the smallest axis of conductivity is paral- 

 lel to the intersection of the planes of most difficult cleavage. 



3. If the planes of cleavage in the same crystal are oblique 

 to each other, the greatest axis of thermal conductivity is 

 the intersection of the angle which includes the mutual in- 

 clination of the planes of easiest cleavage, if both of these 

 planes are equally easy of cleavage; and if they are unequal- 

 ly cleavable, then the greatest axis is at an angular distance 

 from these planes, which varies in the same direction as the 

 plane of easy cleavage. 



Jannettaz also made experiments on fifteen species of schist- 

 ose rocks, and invariably found that heat is conducted with 

 equal facility in all directions in the planes of lamellation of 

 these rocks, but in directions perpendicular to these planes; 

 that is, in sections at right angles to the cleavage, heat is 

 conducted easier in the direction of the cleavage than across 

 the cleavage. In the case of a steatite from the United 

 States, heat is conducted twice as well alono; the line of cleav- 

 aire as across this direction. 



Jannettaz used in his experiment the method of Senar- 

 mont; that is, he coated the section of the mineral with wax, 

 and leading through it a silver wire, whose farther end was 

 heated, he determined the rate of conduction in the plate, 

 outward from the wire, by observation of the isothermal con- 

 tour determined by the melting of the wax. 



In connection with the experiments of Jannettaz, it is in- 

 teresting to know that Fizeau has recently found that schist- 

 ose rocks dilate more in a direction perpendicular to their 

 cleavage than in the direction of the cleavage. Also it has 

 been determined by experiments of the International Metric 

 Commission on a large ingot of platinum, containing ten per 

 cent, of iridium, that the co-efficient of expansion of this bar 

 was increased after having rendered it more dense by sub- 

 jecting it to the action of a trip-hammer ; its co-efficient, from 

 this cause, rising from 0.00000886 to 0.00000902. It was found 

 that after two annealings at a temperature of 1300 C, the 

 co-efficient fell nearly to what it had been before the ingot 

 was hammered. The rolling of metals produces the same ef- 

 fect on them as above described; but wire-drawing a metal 

 reduces its co-efficient of expansion. 



