THE CONSTANTS OF THE CUP ANEMOMETER. 
791 
bearing. Now if we examine Plate 67, fig. 2 , it is obvious that the spindle of the pulley 
G is pressed by the weight W+D ; that of C by the same — friction of G, and 
so on to I. From this the tensions of the cords GO, Cl, and of U, the cord which 
leaves I for the driving pulley can be determined. The same thing can be done for 
U', FK, and HF. Now tension of U — tension of XT' — friction of vertical axle is 
the force which drives the axle ; and if this be worked out, supposing f equal 
in each pulley, and so small that powers above its square may be neglected, we 
have U — l'=XD — (2W-j-D)X t /. When D =12 the axle sometimes moves, but 
seldom; I think 11 is the limit, and as 2 W =120 we have j\ = ) dp and therefore 
r 5-5 ~i 1-025 p 
P= J fD — (2W — F ) X 2 . rq r yoTs’ anc ^ we can ^ yH constant. This proves to be 
the case as is seen in the following table, which gives the results with Nos. I. and II. 
Table Y. 
No. I. 
D 
P 
t'. 
P-tYA 
Xo. of 
Observations. 
22-3 
0-583 
0-004278 
-0-017 
3 
28-5 
0-903 
0-004464 
+ 0-015 
4 
33-8 
1-174 
0-004418 
+ 0-004 
5 
44 
1-700 
0-004531 
+ 0-048 
6 
55 
2-267 
0-004412 
+ 0-006 
7 
64 
2-730 
0-004479 
+ 0-047 
7 
74-3 
3-260 
0-004380 
-0-018 
7 
105 
4-843 
0-004239 
-0-186 
1 
No. II. 
D 
P 
P-£'V 2 . 
No. of 
Observations. 
25-75 
0-760 
0-001332 
-0-051 
4 
28-8 
0-917 
0-001370 
— 0-002 
5 
35-8 
1-277 
0-001383 
— 0-006 
6 
40 
1-507 
0-001332 
-0-062 
6 
48 
1-906 
0-001464 
+ 0-014 
7 
56 
2-318 
0-001441 
+ 0-078 
1 
The agreement is good; for the 9-inch cups e=0'004400; for the 4-inch = (P001387 ; 
and I think it likely that they would answer well even for real wind. 
(22.) The observations for determining a {vide par. 27) show that the effect of v may 
he neglected, as in them v=0. I take three from No. I. 
5 i 
MDOCCLXXVIIL 
