1058 
DR. T. R. ROBINSON ON THE DETERMINATION OF 
No. 
c. 
* 
T. 
15'38 
3-768 
II. 
107-86 
9-537 
III. 
99-83 
4 644 
IV. 
55-11 
3-155 
V. 
48-47 
1-196 
VI. 
60-66 
4-060 
VII. 
63-16 
1-606 
VIII. 
36-39 
1"5925 
IX. 
54-87 
7-393 
X. 
64-98 
5-351 
XI. 
15"05 
0-9625 
XII. 
16-02 
6-331 
XIII. 
23-09 
6-275 
XIV. 
43-58 
4-987 
704-45 
4-854 
sum t/RC 
sum C 
14-984. 
II for mean v= 14*728. 
Correction = + 0 '15 6. 
Even here the error is not of a nature to interfere with the determination of the 
constants, though in such work terms like V. and XI. had better be omitted. If it 
were thought necessary the exact computation is not difficult. 
(61.) At first the additional friction was applied by the brake-levers, and was 
measured by the process described in the note to paragraph (19); but it was soon 
found to be irregular on account of the rusting of the cast-iron disc on which the 
rubbers pressed. This could not be prevented in the present location of the instru¬ 
ment. 
The rust wore off in the course of an experiment and filled the pores of the cloth on 
the rubbers. Yet more, it became evident that the constants which in the whirling 
experiments had given V—W pretty fairly, fail totally here : for instance, with the 
set last given they give Y=14'605, V / =20‘066, the difference being far too great to 
be caused by any error of the friction. 
(62.) I intended to remove the uncertainty caused by the rust by substituting for 
the iron disc one of bell metal of the same diameter; it is, how-ever, some 20 oz. 
heavier, and the normal friction of E is now 30‘4 grains, and its moment =27542. 
But while it was being prepared it occurred to me that instead of measuring the brake 
friction first and assuming its permanence during a series of observations it would be 
better to record and measure it during the entire time of each observation. Peony’s 
brake afforded a ready means of effecting this, and was thus applied: a ring of iron an 
inch deep and -yg inch thick is divided into two semicircles held together by screws 
tapped in the lugs; when these are removed it can be got on the axle, lowered to the 
disc, and is made to clamp it with any required pressure by replacing and tightening 
the screws. The ring has an arm which carries an arc of the same depth concentric 
with the disc and of 8" radius. It is obvious that when the anemometer is turning, 
a cord attached to this arc will be pulled by a force =the moment of the ring friction 
at 8". This pull is measured by a spring balance which I made with one of the clock 
springs described in paragraph (26). 
