GROWTH IN TREES. 11 



the end of the blocks were easily put in place or removed, so that any 

 number of blocks might be joined to form a support which would en- 

 circle a tree of any size. From 4 to 9 blocks were used in most of the 

 instruments. A wooden block of larger size, carrying an upright rod 

 10 cm. long as a support for the recorder, was used to close the support 

 or form the buckle of the belt. The actual fastening, however, con- 

 sisted of a pair of threaded rods extending from the large block and 

 resting in the slots of angle irons on the small end block. Nuts of 

 suitable form could be turned on these threaded rods until a suitable 

 tension had been put on the belt (see fig. 1). A long wooden screw, 

 working in a small block hinged to the outer end of the instrument base, 

 forms a supporting brace as in the other form of support. When such a 

 belt base is drawn tightly about a tree of the sizes measured, the eight 

 or nine blocks used adjust themselves to the irregularities of the trunk, 

 but in general assume a tangential position and press tightly on the 

 bark and cambium internal to it, but the total disturbance by such pres- 

 sure is small and does not affect the changes in the volume of the por- 

 tions of the trunk actually measured, a few centimeters higher. 



The essential feature of the apparatus is the floating frame which 

 makes two contacts with the trunk. One such contact is made by a 

 set screw, carried by this frame, which may be turned to a point 

 where it makes a slight but firm contact on the trunk. The second 

 contact is made by the quartz-bearing rod of the lever-set carried on 

 the floating frame at a point diametrically opposite to the contact 

 screw. Any change of the trunk affecting the distance between the 

 end of the contact screw, which is immovable on the floating frame, 

 and of the sliding quartz rod of the lever system or set would be ex- 

 pressed in the movement of the pen lever which traces a line on the 

 graduated paper sheet carried by the revolving cylinder. 



The first instruments were constructed at a time, during the Great 

 War, when it was impossible to procure the alloys which have a low 

 temperature coefficient. Floating frames of wood and iron were con- 

 structed in a U-shape. The curved ends of the U consisted of a bar 

 of wrought iron, 1 by ^ inches, fastened by bolts to the sides of the U, 

 which were of seasoned oak boiled in paraffin. The oak bars used for 

 the frames of the carriage tops were found suitable for this purpose and 

 (as they were 3 by 2 mm. in cross-section) are sufficiently rigid. The 

 instrument bar was a strap of iron with the ends turned at right angles 

 to be parallel to the wooden bars. These short arms are slotted so 

 that the instrument bar may be fixed in position at a suitable distance 

 from the trunk. Cold would cause the curved iron member of the 

 frame to be drawn toward the tree, and as the turned ends of the 

 instrument bars run from the tree their contraction by cold would 

 cause a movement which would tend to maintain an equal distance 

 between the two and leave uncompensated only the temperature varia- 



