54 ANNUAL OF SCIENTIFIC DISCOVEIIY. 



wood from Puerto Cabello, etc., belong, the ratio is as 1 to 1'GO. In the 

 fourth group it is as 1 to 1'80; and to this division belong Lime, Tamarind, 

 Iron-wood, Poplar, Savanilla (yellow), etc. Hence, the conducting power 

 of all woods in the direction of the fibre exceeds that in the perpendicular 

 direction by no means in a constant manner, but in one which depends 

 upon the nature of the wood. This superiority is in the first group so small, 

 that the warmth in the direction of the fibre traverses a path only a quarter 

 more in length than that traversed in the same time in a perpendicular 

 direction. In the last group, on the other hand, the length of the path in 

 the first direction is about twice that in the perpendicular one. 



In order to investigate the relations of resonance, two rods were cut from 

 each kind of wood the one being taken in the direction of the grain 

 (Langholz), the second perpendicularly across it (Hirnholz). On suspending 

 these rods freely (their length was 470 millims., breadth 20 millims., and thick- 

 ness 8 millims.), and striking them with a stick, the piece cut with the grain 

 always gives a more sonorous tone than the corresponding cross-grain piece. 

 Nevertheless, the difference of resonance in the tones of the width and cross- 

 grain pieces of one and the same wood, of the first of the groups described 

 (say beech), is unmistakably less than the difference between the tones of 

 the with and cross-grain pieces of any member of the second group. In the 

 second group this difference is less than in the third; and in the third, again, 

 less than in the fourth (as with with and cross grain pieces of poplar). 

 When, therefore, the fibres of all kinds of wood are set in vibration, the 

 purity of resonance is greater when such vibrations are transverse than when 

 they occur in other directions (as when the rods are cut across the grain). 

 But this superiority of resonance is not constant ; it depends upon the nature 

 of the wood. The difference in this respect, in the first group of woods, is so 

 small, that the resonance of two with and cross grain pieces resembles that 

 of two not very dissimilar masses of stone when struck. In the last group 

 the difference is so great, that the tone of the with-grain piece, when struck, 

 has a metallic ring, while the dull sound of the cross-grain piece reminds 

 one of a piece of pasteboard when struck. The division of the woods exam- 

 ined, derived from their thermo-conductive power, is accordingly supported 

 by their acoustic relations. 



By supporting the two ends of the rods employed in the above experi- 

 ments, and loading them equally in the middle, the degrees of deflection 

 which they undergo will give us an insight into their structural relations; 

 for the greater their compactness, the greater the resistance they will offer 

 to bending ; and the less compact they are, the more easily they will yield. 

 The difference in vertical height of the middle points of the bent and 

 straight rods was taken as measure of deflection. A lever was employed'to 

 determine this measure, the end of which passed over an enlarged scale, in 

 order that the readings off might be the more exact. The unit of this meas- 

 ure was a matter of indifference, inasmuch as in the comparison to be in- 

 stituted, relations only had to be determined. Although, as was to be 

 expected, in all cases the with-grain piece was much less flexible than the 

 corresponding cross-grain piece, yet an important difference was noticeable 

 in the different groups. This is best seen by calculating the relation between 

 the bending (measured as above described) of the with-grain and that of the 

 cross-grain wood; that is, the same weight being applied (say 100 grs.), by 

 dividing the number given by the lever with the cross-grain piece by that 

 given with the with-grain piece. This relation (called "ratio of deflection " 



