376 
ME. EYAXS OX THE DE^HATIOX OF THE COMPASS 
SUPPLEMEXT. 
[Added dming the of the pax)er.~\ 
In June 1860, prior to the departui'e of the steam-ship Great Eastern on her fii'st 
Atlantic voyage, I was enabled, through the attention and cooperation of the captain. 
John V. Hall, and managing director, T. Bold, Esq., to institute further experiments 
on the changes of the ship’s magnetism, under the same conditions as those already 
recorded as having been made in the Eiver Thames, at Portland, and at Holyhead, in 
September and October 1859. 
Subsequent to the observations made at Holyhead, the Great Eastern rode out a 
violent gale in that harbour, — remarkable as causing the total wi-eck of the ship Royal 
Charter in the immediate neighbourhood, — which necessaiily subjected many parts of 
the hull to severe concussion from the strain on the cables : the ship’s services were then 
confined to the passage to Southampton ; and during the sojourn at that port for the 
following seven months, she quietly swung round the moorings to the tides and variable 
winds. Extensive artificers’ works were latterly performed in the internal equipments. 
These details are worthy of notice, from the striking progressive chminution of the 
ship’s magnetic force, and further tendency to the fore-and-aft dii-ection of the neutral 
points of disturbance which the Southampton observations developed. 
The same Admiralty standard compass haring been placed in the exact position of 
former experiments, the correct magnetic bearing of the extreme point of the Isle of 
Wight, risible from the anchorage (distant 12 miles), was determined from a series of 
astronomical bearings and the known magnetic variation of the place, the necessary 
correction for parallax due to the length of the ship being allowed for the successive 
points of the compass as the ship swung round. 
From the wind prevailing in one direction for several days prior to the departure of 
the Great Eastern, I was only able, although engaged on the 13th, 14th, and 15th of 
.Tune, to obtain the deriations on sixteen and a half consecutive points ; namely, from 
S.S.E., by the South, to N.N.YV. ^ W. : these deviations, resulting from a curve di'awn 
through fifty-one separate determinations, made under highly favourable circumstances, 
were as follows : — 
