OBSERVATIONS ON THE MAGNETIC DIP AND DECLINATION. 349 
I was this day joined in the observations by Mr. J. N. Nicollet. We read the needles 
alternately, and they were raised from their supports and allowed to assume new bear- 
ings between the successive readings. The initials J. N. N. and J. D. G. will show the 
observations made by each of us. The position of the instrument, this morning, was 
slightly changed from that of June 1st, in order to procure a better shade. 
Needle No. 2, gives, with marked end north, 2°. 8. 2 Ao Fgh Se 
WR RMDICOR: ORG AOL iy csmreces sce a 
Dip, by thirty-two observations on needle No.2, . . . . . . . « 71°20'.32 
Nors.~—The precise position of the instrument, during this day’s observations, was fixed by measurement as 
follows, viz.: 
1. From the instrument to the iron gate west of it, measured along the gravelled walk, is 313 feet. This gate 
is 198 fect east of the row of pillars on the east portico of the capitol. 
2. [rom the position of the instrument to the eastern iron gate, measured along the gravelled walk on whose 
south margin the instrument stands, is 261 feet. 
1841, June 4th.— Washington City, D. C. 
te of | Polarity of | Face of Marked |Meansolartime/North end of Needle lSouth end of Needle} Mean of bot h ends Attached itis 
Needle.|markedendInstrument,| side ofobservation.| reads. emit ___.|___ of Needle. | /yhermometer. of 
of needle. of Needle.| HH. M. a: haemo) get sd pacman le cee Deg.|Mins.&Tenths. (Fahrenheit.) | Observer. 
1 ) E E 9.50 a.m.| 70 . 32.5 70.36 70 . 34.2 75° JLN.N. 
a “ «“ «“ 70. 81.5 70. 35.5 70. 33.5 5 D.G. 
“ “ Ww Ww 9.56 7). 16 72.08 #2" 115 76° JENN, 
«“ «“ “ “ 72.16 72. 08 72°. 19 IDG. 
6s “ W E 10.04 71.380 71.23 71. 26:6 veg J.N.N. 
“ «“ «“ «“ 71. 30 71, 24 Fito, J.D.G. 
Md ds E W 10.14 Tok. s ig ey G1. 24 V7 J.N.N. 
“ “ “ «“ 71...21.5 YT, 26 TPQ vi Mee PE EY OF 
1 N E E 10.30 V1, 21 71.27 71. 24.5 77.5 |I.N.N. 
6 “ “ «“ 71 221.5 71. 26 71. 28.7 J.D.G. 
« «“ Ww W | 10.38 71.06 70. 59 71. 02.5 J.N.N,. 
“ “ «“ «“ 71. 06 71. 00.5 7.08.2 J.D.G. 
“ “ Ww E 10.42 71.29 W121 71.25 78 \J.N.N. 
«“ «“ «“ “ 71.28 Yl. 22.6 71 .25.2 J.D. 
«“ “« ia W | 11.00 70. 46.5 70.51 70. 48.7 79 J.N.N, 
«“ perenne ee Pe, See ie a ee ‘|. D.G. 
Needle No. 1, gives, with marked end north,. . . . . 71° 10.16 
mith marked 6nd south, © 0%; i. ok... PL ROS 
Dip, by thirty-two observations on needle No.1, . . .. .... . 71°17.10 
Dip, by thirty-two observations on needle No.2, . . . . . . . . 71° 20'.32 
1841, June 4th.—Dip, near the centre of the public garden, east of the 
capitol, Washington City, by a mean of both needles of Gambey, . . . 71° 18'.7 
The close coincidence of the repeated readings of the needles of this instrument, in the 
various positions necessary for a complete result, induced Mr. Nicollet to express a wish 
that we should institute a comparison, by means of simultaneous observations, between 
the dip, as given by this instrument, and that given by his instrument, made by Robin- 
son, of London, He accordingly sent to Baltimore for his instrument, to be brought to 
Washington by the next morning’s early cars. It arrived early on the morning of June 
5th, and we continued the observations, each using his own instrument, as follows, viz.: 
