DU. TYNDALL ON MOLECULAR INFLUENCES. 
223 
mass in these three directions. It may be remarked that the cubes were fair average 
specimens of the woods, and were in all cases well-seasoned and dry. 
The cube was first placed upon its four supports abed, so that the line of flux from 
iri to m was parallel to the fibre, and the deflection produced by the heat transmitted 
in sixty seconds was observed. The position of the cube was then changed so that 
its fibre stood vertical, the line of flux from m! to m being perpendicular to the fibre 
and parallel to the ligneous layers ; the deflection produced by a minute’s action in 
this case was also determined. Finally, the cube was turned 90° round, its fibre 
being still vertical, so that the line of flux was perpendicular to both fibre and layers, 
and the consequent deflection was observed. In the comparison of these two latter 
directions the chief delicacy of manipulation is necessary. It requires but a rough 
experiment to demonstrate the superior velocity of propagation along the fibre, but 
the velocities in all directions perpendicular to the fibre are so nearly equal that it 
is only by the greatest care and, in the majority of cases, by numerous experiments, 
that a differential action can be securely established. 
The following table contains the results of the inquiry ; it will explain itself. 
Table 1 . — Strength of Current used to heat the bent Wire, as measured by the 
tangent galvanometer : — constantly 35°. Deflections, the line of flux being of:— 
Description of wood. 
I. 
Parallel 
to fibre 
of wood. 
II. 
Perpendicular 
to fibre and 
parallel to lig- 
neous layers. 
III. 
Perpendicular 
to fibre and 
to ligneous 
layers. 
Description of wood. 
I. 
Parallel 
to fibre 
of wood. 
II. 
Perpendicular 
to fibre and 
Darallel to lig- 
neous layers. 
III. 
Perpendicular 
to fibre and 
to ligneous 
layers. 
American Birch 
O 
35 
O 
9 
O 
11 
O 
10-5 
O 
11-0 
9-5 
11-0 
Oak 
33 
9-5 
11 
10-5 
9-5 
8-0 
10-5 
8-0 
11-0 
9-0 
10-0 
Black Ebony 
32 
Mean 9’5 
Mean lO’S 
9-7 
11-2 
9-5 
11-0 
Bird’s-eye Maple ... 
31 
11 
12 
Beech 
33 
Mean 8' 8 
Mean 10‘8 
9-8 
12-0 
10-0 
11-0 
10-2 
12-2 
11-5 
12-0 
10-2 
12-0 
11-0 
13-5 
9-5 
12-0 
Coromandel-wood. 
9-5 
13-0 
Lance-wood 
31 
Mean 10‘6 
Mean 12*1 
An exceedingly hard 
wood from Ceylon 
33 
Mean 9’8 
Mean 12’3 
8*0 
8-0 
10*0 
10-0 
Quebec Pine 
33 
10 
11 
Zebra-wood. 
8-5 
10-0 
1 'I'hp prnrhipp ot’ fhp 
9-8 
11-0 
Brazils 
31 
Mean 8-2 
Mean lO-O 
10-0 
12-0 
Beef-wood. 
10-5 
11-5 
i 
9-8 
12-3 
A red-coloured m'ooc 
9-8 
11-0 
! 
10-0 
11‘7 
from New South 
— 
10-0 
12’0 
Wales 
33 
Mean lO’O 
Mean 11 ‘4 
1 
10-0 
12-0 
i 
Box-wood 
31 
Mean 9'9 
Mean 12*0 
