558 Proceedings of the Royal Irish Academy. 
former, the following results were obtained : both indexes had been 
brought to zero. 
Primary index completed 100° while secondary traversed 30° 
200 „ „ 60 
300 „ „ 94 
When the secondary index had traversed 94°, the primary had passed over 
300°. But the case was very different when the length of gut-line 
exposed was 4^ inches, and the distance of the secondary index to 
clamp same as before. 
Primary index completed 
Differences. 
100° Secondary 11° 
. ir. 
200 
22 
. 11 
300 
31-5 
9 -5 
400 
77 
43 
. 11 -5 
500 
77 
56 
. 13 
600 
7 7 
69 -5 
. 13 -5 
700 
77 
83 
. 13 -5 
800 
77 
97 
. 14 
On one occasion, when the gut-line exposed was 4*65 inches, of 
which I- inch was the distance of the secondary index from the clamp - 
screw which held the gut-line. 
Primary index completed 100° Secondary 10° 
200 
300 
400 
500 
600 
700 
800 
20 
29 
39 
50 
58 
70 
80 
Differences. 
10°. 
10 
9 
10 
11 
8 
12 
10 
In the first case, the primary index completed the circuit of the 
graduated dial three times, while the secondary went round once ; 
for 94° could be recorded only once in a circuit of 100°. In 
the second case, the primary index completed eight circuits, while 
the secondary made the circuit once, and could do no more. 
It may be seen, by these statements, that the untwisting of the 
gut-line is not equable, but is nearly so. The difi'erences 9.8.12 vary 
from the average ; yet no mistake can arise from inspection of the 
hygrometer : for if the secondary index stand at 29° or 39° or 58° on 
the graduated circle, the observer will know that these numbers can 
mean no other than 30°, 40°, or 60°, although a little unevenness in 
the twist of the gut-line causes a trifling disagreement, but for which 
the differences throughout would have been 10°. 
