Wood on 
Photographic Plates. 
97 
No. of 
No . of 
Condition 
Temp, and Time 
Type of Wood . 
Spring . 
Autumn 
PjLUIC /£/ 
Pine. 
Plate. 
of Wood. 
of Exposure. 
Wood. 
Wood. 
229 
T 37 
Moist air 3 days 
40° C. 21 hrs. 
f sap-wood, ) 
£ heart- wood ( 
+ 
158 
Do. 
» 9 6 ,, 
Do. 
+ 
— 
201 
Do. 
„ 24 „ 
Do. 
— 
+ 
T39 
Dried at ioo° C. 
3, 21 „ 
Do. 
So active that no 
detail seen 
145 
Do. 
> » ^ J 3 
Do. 
Slightly + 
+ 
^160 
Do. 
»» 2 4 >» 
Do. 
>3 + 
+ 
283 
283 
Moist air 3 days 
40° C. 48 hrs. 
\ sap-wood, ) 
1 _ 
Fig. 8 
| heart -wood ) 
T 
154 
Do. 
,, 9 6 3. 
Do. 
+ 
— 
193 
Steamed 12 hrs. 
„ 120 „ 
Do. 
+ 
— 
and left 41 days 
Fig. 9 
123 
Dried at ioo° C. 
33 72 ,3 
Do. 
— 
+ 
In 
these 
cases specimens of Scotch 
Pines No. 191 
and 471 
gave 
throughout the spring wood negative and the autumn wood positive, as in 
the Larch, where air-dried timber was used. In these two cases also, where 
the timber has been subjected to ioo° C. for two days, its activity is totally 
altered ; the spring wood becomes positive and the autumn wood negative, 
just as in the specimens given in the first tables. Specimen 229 gave rather 
puzzling results, since plate 1 58 apparently contradicts the other negatives 
obtained. Both plates 158 and 201 are clear and definite negatives, though 
the position of the indicators is much better defined in the latter. The 
piece of specimen 229 which had been dried at ioo°C. for two days 
showed activity all over, so that a very short exposure had to be used to 
obtain any differentiation. Even then the spring wood was still slightly 
active, though not so active as the autumn wood. This, then, is inclined to 
the Larch picture. Specimen 283 shows the Larch image in the case of 
wood dried at ioo° C. for two days, the spring wood being negative and the 
autumn wood positive, whilst the air-dried wood of 283 follows the usual 
trend for Scotch Pines (see Figs. 8 and 9). 
These results cannot depend on the time and temperature of exposure 
or the amount of moisture present, since these varied without any corre- 
sponding variation in the image. The type of wood used — sap-wood or 
heart-wood — does not affect the results, for the specimens which gave results 
consistent with those of Dr. Russell were some heart-wood, some sap-wood, 
and some both. In the same way Scotch Pines Nos. 471 and 191, which 
were consistent in producing the reverse image, were one heart-wood and the 
other sap-wood. 
It was also discovered that if the same piece of wood was used many 
times on photographic plates its activity diminished, so that a piece of 
wood which gave a perfectly good negative at 40° C. in 24 hours at first 
required a time of exposure of 3-4-5 days later on to obtain anything like 
the same intensity. 
I 
