356 OBSERVATIONS ON THE MAGNETIC DIP AND DECLINATION. 
5th. At the observatory in the botanic garden of St. Mary’s College, by 
sixty-four observations on needles No. 1 and 2 combined, on the 11th of 
Gene 1Shigieris vous hse al See ath omens cc een ere oows, ‘bee ere ARE BBY 
Comparing the dip obtained by Professor Bache, at station No. 2, with two needles, 
on the 27th of August, 1840, namely, 71° 34'.4, with my result from sixty-four observa- 
tions, on two needles, on the 10th of June, 1841, namely, 71°32’, we have, for an elapsed 
time of nine and a half months, a diminution of 2’.4, which is very near what might be 
expected in that lapse of time; and hence the agreement of the results obtained by two 
different observers, with different instruments, serves to confirm the accuracy of both. 
Professor Loomis observed the dip in the grove north of the Washington Monument, 
Baltimore, with a single needle, on the 25th of September, 1839, to be 71° 50'.3.* But 
the precise locality of his station is not given. This is to be regretted, because it pre- 
cludes any correct comparison with the results of other observers, and other instruments, 
made at after periods, for the purpose of ascertaining the periodical variation in the dip. 
This grove is an extensive one, and it has been shown, by the observations here pre- 
sented, that a very little change of position in this grove produces a very sensible change 
in the dip. My stations 1, 2, 3, and 4, are all within this grove, which extends north 
and east of the Washington Monument. It is very desirable that all localities for mag- 
netic observations be stated with precision, in reference to permanent and conspicuous 
objects. 
XVIII, OBSERVATIONS FOR THE DIP OF THE MAGNETIC NEEDLE, WITH INSTRUMENT BY 
GAMBEY, OF PARIS. 
Date and place of observation.—1841, June 14th. At the magnetic Observatory of Girard 
College, Philadelphia. 
cual gt ete, tensa eri Noonan hcg] Mena ta 
| of Needle. | | i. M.  _ |Deg.|Mins.&Tenths, Deg. |Mins.fTenths.|Deg.|Mins.gTenths, Fahrenheit.) Observer. 
| -| | 
4 | N E E 4.36P.m.| 72 . OL 72. 00 7. 00.5. A.D.B. 
Po opS 6 “ “ 71. 59 We. Ue 1200.5 | «48> |J.D,G.| 
A de of “ “ 11269 72 . 02 1 oo O00B::+) veh A.D.B. 
dels i le os EES Ss 4,50 F1 y5 ie 71. 26 V1 «24 J.D.G. 
Ge pr 47 7 < “ 71. 24 71. 28 726 77.5 |A.D.B. 
es led i &“ «“ Tht 71, 28 71. 26 J.D.G.| 
= WwW E 5.00 72.19 q2..42 ye ee A.D.B.| 
ool x « “ 72, OU) oie 72-165 75.5 (|J.D.G.! 
«“ «“ «“ «“ 72.18 W944 a2.,46 A.D.B.| 
et; 4 WwW Ww 5.12 71. 46 71.39 71 .42.5 74.2 |J.D.G.| 
fe & “ 71. 40 ye ie eG 71% 41.5 A.D.B.| 
[pe Po eet «“ 71. 46 71, 39:6 Thad “4 J, DG.) 
{ | | e —— 
(i, S| Wo | oon ee 72 . 10 72. 14.5 72.7 |A.D.B. 
| ee eee ec (72.19 72-18 72°16 J. D.G. 
Ls e 5) ee 72.16 72.08 72. 1 IA.D.B. 
| oo) ye Ee) mabe 72. 04 a1, BT 72 . 00.5 71.5 \J.D.G. 
é fois 7 p20 «OW 72.038 71.56 71. 59.5 A.D.B. 
ee eS a a 72.03 71 . 58 72, 00.5 J.D.G. 
, oy “ | E | W | 6.00 71.009, 72.03 Tne 71 A.D.B. 
| 66 | 4 | 66 71°. 38 72) 4302 72 . 00 J.D.G,} 
+ | 6 | bs | 71.09 72-.< 08 hs) VA A.D.B. | 
‘ a PAB che Bio G10 71. 42 71. 47 71. 44.5 70 J.D.G. 
“ | 66 66 | “1. 39 71. 45 71. 42 A.D.B. 
“al ee } «6 6.20 71, 4! 41-46 71.48 J.D.G.| 
* See Transactions of the American Philosophical Society, vol. vii., new series, page 108. 
