MECHANICS AND USEFUL ARTS. 



55 



in the following table) has, in the first group, the mean value of 1 to 5: in 

 the second, 1 to 8; in the third, 1 to 9.5; in the fourth, 1 to 14. The divis- 

 ion of the groups is therefore also supported from this point of view.* The 

 difference in the structure in the different directions is least in those woods 

 which show the least difference with respect to direction in their thermo- 

 conductive and resonant properties; and the difference in the former is 

 greater or less as the two latter differences are greater or less. 



Hence a definite relation may be established between the different phe- 

 nomena described; and this is true to such an extent, that the knowledge of 

 one of them, z. g., the mechanical or state of cohesion, is sufficient to deduce 

 the others, those of warmth or resonance. 



Thus, merely to adduce one example, especial experiments had shown 

 that in petrified woods a difference of structure in the directions parallel 

 with, and perpendicular to, the direction of the grain had been preserved; 

 and, in fact, the thermal curve was an ellipse whose major axis was parallel 

 to the fibres. As in the petrified example, this difference in mechanical 

 structure was much less than in the living wood; so, also, while in the living 

 Conifer the ratio of the axes was as 1 to 1.80, in the petrified specimen it 

 had sunk to 1 to 1.12. 



The following table contains the names of the woods examined, arranged 

 according to the groups mentioned : 



GROUP I. 



Ratio of the axes of the thermal ellipse 1 to 1-25. 



Mean ratio of deflection 1 to5'0. 



Acacia. 

 Box. 



Lignum-vitas. 

 Cypress. 



Ratio of axes of thermal ellipse 



Elder. 



Alder. 



White Thorn. 



Arbor-vitae. 



St. Lucian wood. 



Gymnodadus canadensis. 



Beech (2 species, white and red). 



Plane. 



Elm. 



Oak (two species). 



Ash. 



Maple. 



American maple. 



Cedar of Lebanon. 



Australian cedar. 



Mahogany. 



Palisander. 



Ebony. 



Palm. 



Rosewood. 



King wood. 

 Satin wood. 

 Salisburia ( Gingho). 



GHOTJP- II. 



1 to 1-45. Mean ratio of deflection 1 to 8'0. 

 Snake wood. 

 Zebra wood. 



Purple wood (Amarantkus). 

 Settin. 



Coromandel wood. 

 Angica wood. 

 Cocoa wood ( Gateado). 

 Apple. 

 Pear. 

 Cherry. 

 Plum. 



Sandal (red). 

 Caliatour. 



Costarica (red wood). 

 Bimas sapan. 

 Cuba (yellow wood). 

 Viset (yellow wood). 

 Cnmpeachy blue wood. 

 Tobasco blue wood. 

 Domingo blue wood. 



* The diversity of rattire, even with one and the same kind of wood, of course 

 did not admit of the boundaries of the groups being drawn with great exactness, 

 or of the subdivision of the groups into secondary ones. 



