1912] BOVIE—PRECISION AUXANOMETER 507 
The escapement should be such that one (and only one) tooth of the 
escapement wheel can pass at one closing of the circuit. This 
becomes important when the screw has to make a complete revolu- 
tion for each record. 
The chronograph was constructed especially for this apparatus. 
The drum turns once in six hours, and is of such a diameter that 
I mm. on the drum corresponds to one minute in time. The drum 
is long enough to receive the records from six auxanometers at one 
time, and holds one week’s record. The pens are stationary, the 
drum turning under them and moving forward in the line of its own 
axis, so that each pen traces a spiral on the record sheet. At each 
closing of the circuit the pen makes a check in the line traced. 
en the record is removed for reading, we have a series of parallel 
lines, each representing six hours of time. By counting the number 
of checks in a given length of time, or by measuring the distance 
between the checks, the rate of growth can be determined. 
By means of a small switchboard, an electric bell or an electric 
light can be included in the circuit, so that each time an increment 
of growth is recorded the light flashes and the bell rings. This is 
used only for lecture experiments. A tungsten lamp should be 
employed, as the length of contact is so short that an Edison lamp 
does not have time to become luminous. 
An elongating hyacinth peduncle, which had been in the damp 
greenhouse and was removed to the dry air of the lecture-room, gave 
a record a little oftener than once a minute. Had the plant been 
left in the greenhouse and only the chronograph taken to the 
lecture-room, the contacts would have been more frequent. A 
young sunflower seedling gave a record every 18 seconds. Such 
records are too frequent for experiments of long duration, as there 
are too many checks to count. When working with plants growing 
at this rate, some of the teeth in the escapement wheel should be 
removed. 
The principle of having the plant automatically close and open 
an electric circuit during growth permits the increase in length to 
be measured to almost any degree of accuracy. The only difficulty 
is a tendency to arcing across the spark gap between the spring 6 
and the block c. There are two ways of preventing this: the wire 
