404 
MR. W. CROOKES ON THE VISCOSITY 
the arcs, to get the equilibrium readings for the force arising from the candle supposed 
constant during that swing, and equal to what it was in the middle of the swing. 
The following is an example of the observations which I have plotted above, treated 
way : — 
Log. dec. 0’066 ; 
L. 1 + N 0-33; 
5. 
Reading. 
Arc. 
Log. arc. 
Less 0 335. 
Humber. 
Zero for siring. 
I. 
II. 
III. 
IV. 
V. 
VI. 
88 
88 
T944 
1-609 
40-6 
47"4 
29 
59 
1-771 
1-436 
27-3 
56-3 
83 
54 
1-732 
1-397 
24-8 
58-2 
32 
51 
1-708 
1-373 
23-6 
55"6 
75 
43 
1-633 
1-298 
19-9 
55T 
40 
35 
1-544 
1-209 
16-2 
56-2 
68 
28 
1-447 
1112 
12-9 
55T 
Mean.55'9 
The numbers in column VI. are obtained by applying column Y. to column I., 
by subtraction and addition alternately. The first figures are marked off with a 
line, because the method gives only a rude approximation for the first swing, as the 
whole of the force, very nearly, has grown during this swing. 
657. With a high logarithmic decrement the process just given should always be 
used ; but with a low logarithmic decrement, as in the example, it may be simplified 
by taking the mean of consecutive arcs, then the half means, and then applying these 
fi- and — to the successive readings, as in the following example :— 
Reading. 
Swing. 
Arithmetical 
Half of III. 
Applied + and — to I. = approx¬ 
imate calculated position of 
I. 
II. 
III. 
IV. 
equilibrium. 
V. 
0 
88 
88 
735 
36"7 
52-1 
29 
59 
56 - 5 
28-2 
57-2 
83 
54 
52-5 
26-2 
56-8 
32 
51 
47-0 
23-5 
55"5 
75 
43 
39-0 
19-5 
55-5 
40 
35 
31-5 
157 
55'7 
28 
Mean . 
.... 56-1 
1 have cut off the first swing, which is clearly out of series. The slight diminution 
of the last three, as compared with the second and third numbers, may not improbably 
