18 SEVENTH REPORT—1837. 
derived from the observations in the first table ;—and the result- 
ing intensity at the station relatively to Rio. The contents of 
the tables thus far are the results of Capt. King’s observations, 
unmixed with those of any other observer. We have now 
to express his results in terms of the general scale of compari- 
son, and this is done in the final column, by taking the value 
of the intensity at Rio at 0°884, which is the mean of four inde- 
pendent determinations by the following observers, viz. : 
1817 and 1820 Freycinet . . . 0°890 
1827... 6s. Litke seis 0°886 
TE6B0 6 cs Erman .... 0:879 
1836 oa a Fitz Roy ... 0°878 
I have included in table II. Madeira and Port Praya, at which 
Capt. King observed in his outward passage. The dates of 
these fall between the observations at Greenwich in March, 
1826, (corrected time = 734-0 and dip 69° 52',) and those at 
Rio in August, 1826. Having the intensity at Greenwich 
= 1°372 and at Rio = 0°884, we have the time of vibration 
as a dipping-needle at Rio at the respective dates as follows: 
March, 1826 ...... 536°2 
August, 1826 ..... 537-0 
It appears, therefore, that only a very slight change took 
_place in the magnetism of the needle during the outward voy- 
age, and we may take 536°6 as the time of vibration at Rio, 
corresponding to the dates of the observations at Madeira and 
Port Praya. I have assumed the dip and force at Greenwich 
to be the same as at London. The dip at Madeira was not ob- 
served by Capt. King, but has been supplied from my own ob- 
servations in 1822, which were made in the same locality, 
namely, the Consul’s garden in Funchal, where Capt. King’s 
needle was vibrated. I have deducted 12' from my determina- 
tion of the dip at Madeira for the probable change between 
1822 and 1826. 
Taste I. 
Time of Vibration. 
Rio de Janeiro 3 
; 7 is Int 1, Loss. Per diem, 
wg Bg i Horizontal. As pe care rn brs 
Ss. s. Days. Ss. 
August 29, 1826...| 545°2 537°0 
i 382 | 65 017 
September 15, 1827 5518 543°5 
} 462 | 92 020 
December 21, 1828 561-1 552-7 
i 507 | 27 005 
June 1, 1830 ...... 5638 555-4 
