THE CONSTANTS OP THE CUP ANEMOMETER. 
1067 
Omitting the first five S(V — V') = — 3T79, Se'=269'80. Hence Ax= — 0'0117 and 
x= 1*8624 and z=2'468 and the limit = 3'436. This result surprised me, for the 
friction was so small that no irregularity of it could have any sensible influence, nor 
does it seem probable that the pressures on the surfaces of the two sets of cups are in 
any other ratio than that of the surfaces. The x is actually larger than that of E.,. 
The five first V's were computed with the final x. They give V' rather too small, 
but in three of them the wind was S.W. 
(76.) E 6 . I now placed my old anemometer, cups 12", arms 23"'17, on the axle 
of E. The a of these cups (if as their area)=27'227* and their y=29'0. With 
the second approximation, £c=l‘5897, 2=1 '527, I recomputed the V and V' of 
Table XXYI. 
Table XXVJ. 
No. 
Dir. 
Time. 
A. 
A'. 
Log. <p'. 
V . 
v'. 
V. 
V'. 
V-V'. 
I. 
N.W. 
600 
313 
339 
0-05547 
4-470 
4-674 
12-737 
13-415 
-0-678 
II. 
N. 
600 
332-5 
386-5 
0-04264 
4-747 
5-328 
13519 
15-133 
-1-614 
III. 
N. 
1200 
695 
784 
0-05223 
4-962 
5-404 
14-122 
15-351 
-1-229 
IV. 
N. b. E. 
600 
240 
286 
0-04524 
3-427 
3 943 
9-809 
11-247 
-1-438 
V. 
N.E. 
600 
382 
378 
0-04701 
5-455 
5-211 
15-509 
14-806 
+ 0-703 
VI. 
W. b. N. 
600 
292 
300 
0 05411 
4-170 
4-136 
11-896 
11-795 
+ 0-101 
VII. 
S.W. 
600 
398 
368 
0-05435 
5-683 
5-074 
16379 
14-404 
+ 1-975 
VIII. 
S.E. 
600 
751 
783 
0 05273 
10-725 
10-796 
30-392 
30-464 
-0-072 
IX. 
S. 
600 
726 
751-7 
0-05918 
8 640 
8-636 
24-499 
24-484 
+ 0-015 
X. 
S. 
660 
620 
615-8 
0-05918 
8-048 
7-778 
22-830 
22-014 
+ 0-816 
XI. 
S. 
660 
659 
679-6 
0-05918 
8-555 
8-517 
24-261 
24-120 
+ 0141 
XII. 
S. 
660 
502 
516-7 
0-05918 
6"516 
6-476 
18-506 
18-365 
+ 0-141 
XIII. 
N.E. 
600 
286 
282 
0 > 04772 
4-277 
3-887 
11-652 
11-591 
+ 0-06 L 
XIV. 
E. 
600 
340 
329 
0-04556 
4-855 
4-535 
15-497 
12-900 
•+■ 2*59 / 
XV. 
E. 
600 
358 
34S-5 
0-04833 
5-112 
4-935 
14-454 
14-037 
+ 0-417 
XVI. 
E. 
1200 
793 
860 
0-04435 
5-662 
5-928 
16-093 
16-890 
-0 797 
XVII. 
N.E. b. E. 
600 
279-7 
294-5 
0-04666 
3-994 
4-060 
11-399 
11-578 
-0-179 
XVIII. 
N.E. b. E. 
600 
278-5 
277-8 
0-04797 
3-977 
3-830 
11-351 
10 934 
+ 0-417 
It will be observed here, as in Table XX., that v is sometimes greater, sometimes 
less than v; the near equality of the constants of the 12" cups to those of K makes 
the irregularities of the wind manifest.f The S (V—V') giving III. and XVI. (double 
weight) = — 0'649, Se'=282'65, therefore dx— — 0‘0023, a?=l'5874, z=l'520, and the 
limit 2'8202. This x is a little less than that of K ; which shows that the influence 
of the diameter of the cups is felt even here, overpowering the effect of the shorter ones. 
(77.) I shall conclude with a few remarks on the preceding results. 
The process by which the x of K is determined seems liable to but two objections : 
* In my original paper “ On the Cup Anemometer ” (Trans. R.I.A., vol. xxii., p. 170) I have mentioned 
some trials to measure «. As the V’s given there were doubtful, I have recomputed them with these 
constants and the friction of that instrument = 48-61. The six give for a, (at normal pressure and 
temperature) 27"898, agreeing fairly with that given in the text. 
f I may mention here, as further proof of the unsteadiness of the wind, that on one occasion I reversed 
two cups of this anemometer so that all the convexes were opposed to the wind; I expected they would 
remain at rest, but they were in continual oscillation through many degrees, so that in the limited area 
5' X 1’ there must have been differences of Y able to overcome a friction of 53 grains. 
6x2 
