A SIMPLIFIED PRECISION AUXANOMETER 
W. T. BoviE 
In a former paper^ the writer described a precision auxanometer 
capable of registering very small increments of growth. The improved 
auxanometer here described wcrks on the same piinciple as the pre- 
viously described instrument. It consists essentially of a device 
which is carried upwards as the plant grows. When the device has 
moved a certain distance, it closes an electric circuit, which operates 
the recording pen of a chronograph. As pointed out in the paper 
referred to above, this arrangement makes it possible to have the 
recording mechanism at any desired distance from the p^ant and also 
to make simultaneous records of a number of plants or of various 
parts of the same plant. 
The design of the instrument has been changed in order to make it 
suitable for the class room. The new auxanometer is light, compact, 
easily and quickly attached to the plant, and, as the force of gravity 
is not utilized for moving any of its parts, it may be set at any angle 
with the vertical, so that growth in any direction may be measured 
and recorded. A slight change in the electrical mechanism has made 
the instrument more reliable. The experimental model ran the entire 
summer in the garden exposed to the weather, the brass case being 
open part of the time so that the internal mechanism was exposed. 
A rack and pinion has been substituted for the micrometer screw 
and nut of the instrument described in 1912. This change has been 
made in order to lower the cost of manufacture. For special research 
work, where records of very small variations in the rate of growth are 
to be made, the micrometer screw model should be used; but it has 
been found that for class work, and for research work where great 
precision is unnecessary, the rack and pinion gives satisfactory results. 
In the instrument with the micrometer screw the escapement wheel is 
fastened to the top of the micrometer screw and consequently the 
control of the motion of the micrometer screw is positive. As will be 
seen presently, the instrument described here does not possess this 
1 Bot. Gaz. 53: 504-509. 1912. 
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