27i 



the source to the opposite face; the quantity transmitted to the 

 opposite face at the end of a minute, will of course depend on the 

 conductivity of the body in the given direction. This quantity is 

 measured by its effect upon the galvanometer. 



The temperature of the source will, of course, depend upon the 

 amount of electricity transmitted through the bent wire, and to pre- 

 serve this amount perfectly constant from day to day, a tangent 

 galvanometer and rheostat are introduced into the voltaic circuit ; a 

 current which produces the invariable deflection of 35° is made use of 

 to heat the wire. By this arrangement experiments M'hich are 

 separated from each other by long intervals of time are rendered 

 strictly comparable. 



In the manner above indicated, the author has submitted fifty- 

 four different kinds of wood, both English and foreign, to examina- 

 tion. The cubes were taken so that four faces of each were parallel 

 to the fibre, and the remaining two consequently perpendicular to it. 

 Of the four parallel to the fibre, two opposite ones were parallel to 

 the ligneous layers, and the other two perpendicular to them. The 

 amount of heat transmitted in 60 seconds across the mass of each 

 cube in these three directions, respectively, was determined in the 

 way described, and the following law of action established : — 



At all points except the centre of the tree^ wood possesses three un- 

 equal axes of calorific conduction which are at right angles to each 

 other. The first and greatest axis is parallel to the fibre ; the second 

 axis is perpendicular to the fibre, and to the annual lasers of the wood ; 

 while the third and least axis is perpendicular to the fibres and parallel 

 to the layers. It is observed that these axes of calorific conduction 

 coincide in order of magnitude and in direction with the axes of 

 elasticity discovered by Savart. 



The author furthermore points out the existence of two other 

 systems of axes in wood, — the axes of cohesion and the axes of fluid 

 permeability, both of which coincide with the axes of calorific con- 

 duction. 



Experiments have been made on the conductivity of various other 

 bodies, and the non-conducting powers of the substances which enter 

 into the composition of organic tissues is strikingly exhibited. From 

 comparative experiments with quartz and some other substances, the 

 author points out the influence which a mass of silica exposed to the 

 sun's rays, as in the African deserts, must exert upon climate. 



The paper concludes with experiments on some other organic 

 structures : Tooth of Walrus, Tooth of Elephant, Whalebone, Rhi- 

 noceros's-horn, Cow's-horn ; and which show how small is their trans- 

 missive power : that of sealing-wax, bees'-wax, sole-leather, glue, 

 gutta-percha. India-rubber, filbert-kernel, almond-kernel, boiled ham- 

 muscle, raw veal-muscle, appears to be unappreciable by the method 

 described. 



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