368 OBSERVATIONS ON THE MAGNETIC DIP AND DECLINATION. 
Weather clear and pleasant. A moderate south-west breeze. 
All the observations at Portsmouth were made under a tent, with fixtures devoid of iron. 
XLI. May 10th, 1844.—Philadelphia. 
Rittenhouse Square. The position of the instrument is the most western point of the 
circular gravelled walk which surrounds the centre grass plat of this square. A wooden 
fence at this time encloses the square. At the centre point of the square is an iron water 
pipe and plug which obliged me to occupy a point without its.influence upon the needles. 
satitude 39° 56’ 59”; Longitude 75° 10’ 43’.5, 
Neep.e No. 1. 
Marked end Readings. Observation, Temperature Dip observed. 
N 16 6h. 57m., A.M. 57° 72° 06! 
Ss 16 ay, - 62 pie 4 
Dip, by thirty-two observations on needle No.1, . . . . . . 72°08’ 
NeEeEDLE No. 2. 
N 16 8h. 58m., A.M. 622.5, Ved 12 
Ss 16 9 38 i 64 5 72° 09.75 
Dip, by thirty-two observations on needle No.2, . . . . . GRE 48 
Dip, by a mean of sixty-four observations on needles Nos. 1 aad mr os see ee 
Weather clear and pleasant, with a gentle easterly breeze aunty the observations. 
The instrument was well shaded by trees. 
Note.—This square affords a very eligible position for magnetic observations. Its centre is sufficiently remote 
from buildings and all cause of extraneous influence upon the needles. ‘The trees within the square afford good 
shade for the instrument, and if the observer choose an early hour of the morning for his observations, there is 
no danger of any interruption from a crowd. 
XLIT. 1844, July 8th.— Washington City, District of Columbia. 
Near the centre of the public garden, immediately east of the capitol. This is the 
same station as XII., where I observed the dip with the same instrument and needles on 
~ the ist, 4th, and 5th of June, 1841. Latitude 38° 53’ 30”, N.; Longitude 77° 01’ 30”, W. 
Neepue No. 1. 
Ss 16 6h. 23m., A.M. 66° 71° 13'.34 
N 16 1 Ocly 4 70 71° 09'.15 
Dip, by thirty-two observations on needle No.1, . . . . . . 71° 11'.24 
NEEDLE No. 2. 
Ss 16 8h. O5m., A.M. 74° 71° 06'.28 
N 16 8 . 56 x 76 Ti vie 47 
Dip, by thirty-two observations on needle No.2, . . . . . .. 71° 09'.87 
Dip, by a mean of sixty-four observations on needles Nos. 1 and2,. . . . 71° 10.55 
Weather fair and pleasant. <A very gentle wind from east-north-east. 
The dip, by a mean of one hundred and ninety-two observations, with this instrument, 
using the same needles as now, was observed on the Ist, 4th, and 5th of June, 1841, by 
Mr. J. N. Nicollet and myself to be 71° 15.9, Mr. Nicollet having joined in hove of 
