78 
MR. AIRY ON THE OBSERVED DEVIATIONS OF THE COMPASS 
2. Wood-built Steamers. 
The Virago. 
18. H+Nx 9-67= +0-493 S= +0-05.5 
19. H—Nx 5-23= +0-029 S= + 0-079 
S presents no sufficient evidence of change. H and N are both positive: and 
the correction of polar-magnet-deviation would be made, either by a magnet with 
marked end towards the head, and soft iron as is described for the Erebus, or by an 
adjustible magnet. 
The Plumper. 
20. H+Nx'9-63= +0-402 S= +0-069 
21. H — Nx2-54 = + 0-301 S=+0-091 
The remarks on the Virago apply also to the Plumper. 
3. Iron-huilt Steamers. 
The Bloodhound. 
6. 
H + Nx9-67=+0-997 
S=— 0-153 
/• 
H+Nx 7*34= + 1-043 
S=— 0-209 
8. 
H+Nx 6-85 = +0-931 
S=— 0-220 
The evidence for a distinct value of N is not very clear. There seem to have been 
changes in the values of H and S (subpermanent magnetism) which on the whole 
would produce, at the stations Nos. 7 and 8, a maximum deviation of nearly 1°. The 
correction of polar-magnet-deviation should be made by adjustible magnets. 
The Jackal. 
9. H + Nx9-67= + l-157 S=— 0-123 
10. H+Nx9-19= + l-005 S=— 0-162 
11. H+Nx 6-85 = + 1-084 S= -0-082 
The remarks on the Bloodhound will nearly apply to the Jackal. The changes in 
H and S would produce at the stations Nos. 10 and 11 a maximum deviation of a 
little more tlian 1°. 
The Trident. 
12. 
H + Nx9-66 = + 1-419 
S= +0-080 
13. 
H+Nx7'03 = + 1-402 
S=— 0-091 
24. 
H + Nx 9-66 = + 1-323 
S= -0-175 
25. 
H-Nx l-49= + l-418 
S=— 0-198 
There seems to be good reason for thinking that N is insensible, that H has not 
sensibly changed, but that S has changed gradually, in the course of several years, 
