Haines. — A New Auxanometer. 
1 87 
This, and the equation for the magnification, namely 
are the only equations needed in the practical work. 
A brief outline will now be given of the method of manipulation of the 
instrument. The chief points in the preparation for an experiment may be 
enumerated as follows : 
1. Weigh the pulley C. 
2. Connect the fibres Q, R, and U with grooves on E which give the 
desired magnification. 
3. Place the plant in position and measure the distance Y from its 
apex to the pulley A. 
4. Find the sum of the lengths x and Z by measuring from the centre 
of E to the centre of B, and subtracting the length of the mounting of C. 
5. Calculate ^ + Y + z, and move the pulley O until X 1 + x 2 = x + Y + z. 
(During these operations, pulleys which have loose threads on them maybe 
clamped, if necessary, by special provisions to prevent them being turned by 
unbalanced weights.) 
6. Attach the weights V and v'. 
7. Find the weight w 1 with the trolley detached. 
8. Find the weight w 2 which turns all the pulleys when the trolley is 
attached to E. The value of w 2 may be incorrect for two reasons : (a) the 
friction of the pulleys A and B will be less than during the experiment, as 
the weights w and w z are not yet in place, and (h) because the friction of 
the pen L on the drum will be greater than during the experiment as the 
drum is at rest instead of in motion. As the weights W and w z are very 
small compared with the other weights producing friction in A and B, namely, 
V, v', c, and D, the difference in friction values due to their absence will be 
practically negligible, and the speed of revolution of the drum being also 
very small, the two errors may be taken as counterbalancing one another. 
If they do not counterbalance, the calculated value of W will be too small 
(assuming the errors due to friction in A and B to be the most serious), and 
W may be increased by a few milligrammes at the beginning of the experi- 
ment. This will overcome the friction of A and O, and so restore the slight 
tension in the thread Y. 
9. Calculate the value of t and the tension in z due to t alone 
(i.e. — - * R V Counterbalance this tension by a suitable weight placed in 
the scale-pan at w v Also use the equation to find W. If the value found 
be suitable, place the weight in the scale-pan ; if unsuitable, repeat the 
operation with a different value for V and v'. 
10. Attach Y to the growing point. 
11. Adjust O very slightly until F is at the correct end of the drum. 
