LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
13 
servations which should be subsequently made. The times of vibration commencing 
with 40° are those inserted in this Table ; the series commencing with 20° will be 
found in its due succession. 
Table II. — Comparison of the Intensity Needles at Panama in October 
1838, and March 1839*. 
Periods. 
Designation of the Needles. 
5. 
7. 
8. 
9. 
11. 
12. 
13. 
October 1838. . . . 
March 1839 
s 
475- 2 
476- 3 
s 
536-8 
536-1 
s 
471-4 
471-4 
s 
439-5 
438-2 
s 
475-8 
474-8 
s 
403- 7 
404- 6 
s 
395-5 
394-5 
This comparison having shown that the seven needles specified in the Table were 
in a steady magnetic state, Captain Belcher despatched Nos. 7- 8. and 9. to England, 
to have their times of vibration observed there, and to be returned to him on the coast 
of California ; purposing by this means to attach his series of relative determinations 
to the great body of results obtained by other observers. The needles were received 
by me in August 1839, and were vibrated on the 12th and 13th of August at a suit- 
able place near Woolwich, where I also observed the dip at the same time. They 
reached Captain Belcher again in the following November at Mazatlan. In the 
meantime the Sulphur had quitted Panama, having on board Nos. 5. 11. 12. and 13, 
and had visited successively Cocos Island, Oahu one of the Sandwich Islands, Kodiack 
and Sitka on the north-west coast of America, Fort Vancouver and Baker’s Bay in 
Columbia River, Port Bodega, San Francisco, Monterey, S ta Barbara, San Pedro, San 
Diego, San Quentin, San Bartholomew, Magdalena Bay, and St. Lucas Bay, arriving 
at Mazatlan in November. At each of the above-named stations the times of vibration 
of one or more of the needles were observed, and occasionally of all the four. On 
the arrival of the three needles which had been sent to England, their times of vibra- 
tion were observed, in comparison with the others, first at Mazatlan, and a few days 
afterwards at San Bias, where, more time being available, the comparison was re- 
peated on two different days, viz. on the 6th and 19th of December. From San Bias 
* Nos. 1. 3. and 4. are not included in this Table, because the observations on the 16th of March 1839 
showed that they were still losing magnetism, and they were not therefore subsequently employed. No. 6. is 
also omitted, and the cause is explained by a memorandum of Captain Belcher’s to the following effect : 
“ No. 6. kept well during the first twenty-one months, and changed suddenly during an excursion to Conchagua 
in November and December 1838. It was vibrated on the 20th and 22nd of November, and gave consistent 
results : on the 27th it was carried on horseback up the Amapola hill, 3000 feet above the sea, and on its return 
on the 22nd of December was found to have lost magnetism equivalent to upwards of 12 seconds in 510 seconds. 
The surface rock on the Amapola hill was so highly magnetic that no satisfactory observations could be ob- 
tained there with the needle.” An examination of the subsequent observations of No. 6, compared with those 
of the other needles, shows that its magnetism was unsteady for many months after this accident, becoming 
gradually weaker. I have not, therefore, taken into account the observations with this needle, as they do not 
yield independent results of equal value with the other needles, and there are enough consistent determinations 
without them. 
