34 SEVENTH REPORT—1837. 
and Greenland, and has been allowed for accordingly ; Orkney 
being compared with the first London rate, Greenland and 
Labrador with the second. ‘The needles then give every- 
where very nearly identical results. 
The dip circle which Capt. Ross employed was of 4 inches 
diameter. The needle appears to have given very consistent 
results always at the same station; for example, of six obser- 
vations at Westbourn-green near London in 1856, the ex- 
tremes are 69° 28’ and 69° 85"6, the poles being changed in 
every observation; the mean of the six, however, as well as 
each of the separate results, is a few minutes higher than the 
dip at that spot is known to have been at that time. ‘Taking 
into account Capt. Ross’s experience in observations of this 
. kind, and that the observations were made on four different 
days, it is most probable that there was some instrumental 
cause for this needle giving constantly at this station a higher 
dip than the truth. Being ignorant, however, what that cause 
may have been, I have not ventured to apply a correction to 
the dips with this needle either there or elsewhere, but have em- 
ployed them just as they were observed at each of the stations. 
In countries where the dip is so great as in the vicinity of 
Davis’s Straits, the horizontal intensities may be very correctly 
determined, and yet from slight errors in the dip, the resulting 
total intensity may present anomalies unusual elsewhere. We 
have an instance of this in Capt. Ross’s observations in Green- 
land. There are two stations in Greenland, at no great distance 
apart, where the difference of the computed intensity is excess- 
ive; and the fact of there being some anomaly in the observed 
dips which would sufficiently explain the difference, is made 
quite obvious by the circumstance that the higher dip is at 
the southernmost station; whereas the dip should increase 
in going northward on this coast, and with this the horizontal 
vibrations are in accord. J have therefore omitted both the 
results in Greenland in the general table. 
As these observations have not been published elsewhere, 
I subjoin a table containing the principal particulars. 
Time of horiz. vibra, Di Ee 
- 1 di 
Station, Date. Lat. | Long. ee) dod cbnerredtite 178. 
De 2 itty ot S. a o 7 
London...... Aug., 1835) 51 31/859 50) 439-07 | 441°46 |.........08 1:372 
Stromness...| Feb., 1836/58 58 |356 80) 480-22 | 483-34 | 73 36 1-419 
Greenlanad | June, 1836/ 66 57 |306 26) 648-57 | 645:30 | 82 51 1:798 
June, 1836/68 59/3806 47| 667-29 | 665-94 | 82 25 1-590 
Labrador ...| Aug., 1836/57 33/298 9} 616-11 | ......... 73 386 1-652 
London...... ct, 1836/51 31/859 50) 442:19 | 441-64 | 69 32:1) 1372 
The times of vibration are reduced toa standard temperature. 
oF ee oe 
