CHEMICAL SCIENCE. 189 



the opposite face in a minute of time. This quantity will of course 

 depend upon conductive power of the wood in the given direction. 

 To measure it, a new instrument has been devised by Dr. Tyndall, 

 whose indications are capable of extreme accuracy. This instrument 

 has very little in common with Fourier's thermometer of contact. It 

 is applied to ascertain the velocity of the transmission of heat through 

 either solids or liquids. The mass to be examined is reduced to the 

 cubical form, and the instrument enables us to bring a source of heat 

 of a strictly measurable character against one face of the cube, and to 

 determine the relative quantity transmitted to the opposite face in a 

 given time. By means of this instrument which the Doctor 

 minutely described the author examined the conductivity of various 

 bodies. Fifty-seven different kinds of wood have been examined by 

 means of this instrument ; the heat travels w r ith a maximum velocity 

 along the fibre, but its flux is not the same in all directions perpen- 

 dicular to the fibre ; it travels with greater speed across the ligneous 

 layers than along them. The complete law of action may be 

 expressed as follows : At all points situate in the centre of growth, 

 wood possesses three unequal axes of calorific conduction, which are 

 at right angles to each other. The first and greatest axis is parallel 

 to the fibre ; the second and intermediate axis is perpendicular to the 

 fibre, and also perpendicular to the ligneous layers ; while the third 

 and least axis is perpendicular to the fibre and parallel to the layers. 

 Dr. Tyndall further shows that in this single substance there are 1 four 1 

 systems of axes coinciding with each other. The axes of elasticity, 

 established by Savart, and the axes of calorific conduction, of fluid 

 permeability and of cohesion, established by himself. Wood, in fact, 

 furnishes us with one of the most instructive examples of the influ- 

 ence of molecular aggregation with w r hich we are acquainted. 

 Among crystalline bodies, rock crystal or fine silica is the best con- 

 ductor. While wood at the end of a minute causes only a deflection of 

 10 or 12, a cube of silica of the same size produces a deflection of 

 90. This fact accounts for the steadiness of temperature in one-set 

 districts, and the extremes of heat and cold presented by day and 

 night on such sandy wastes as Sahara. The sand, which is for the 

 most part silica, speedily drinks in the noon-day heat, and loses it by 

 night just as speedily. Muscular tissue is an extremely bad conductor ; 

 and to this, in a great measure, the constancy of temperature of the 

 human body in various zones is to be attributed. To this fact also Sir 

 Charles Blagden and Chantrey owed their safety in exposing their 

 bodies to a high temperature ; owing to the almost impervious charac- 

 ter of the tissues of the body the irritation produced was confined to 

 the surface. 



ON THE ATOMIC WEIGHTS OF PLATINUM AND BARIUM. 



AT the British Association, Dr. Andrews read a paper on the 

 above subject. Xo determination of the atomic weight of platinum 

 having been made since the recent revision of atomic weights, and 



