OBSERVATIONS ON THE MAGNETIC DIP AND DECLINATION. 355 
From the results at stations three and four, it appears that the needle was not influ- 
enced by the line of iron pipes, for such an influence would have given a less dip than 
at stations one and two, whereas a greater dip was in both cases obtained than that 
observed at either station one or station two. 
Stations three and four are much below the level of one and two. The needles at 
those two stations being in closer proximity to the rocks forming the substratum here, a 
ferruginous sandstone, no doubt caused the great change of: dip; by a slight change of 
position. The dip at these four stations is, indeed, in proportion to the depression of 
these stations, respectively, below a given horizontel. plane. That is, the greatest dip is 
found at the least elevation above ile, and the least dip is found at the greatest elevation, 
and soon, in proportion to actual depression. 
X VIL. Baltimore—Fifth Station.—June 11th, 1841. 
In the small observatory in the botanic garden of St. Mary’s College. This obser- 
vatory was erected for magnetic observations. It is built with copper nails, and there is 
no iron about it. Latitude 39° 17’ 55”, N.; longitude 76° 37’ 30”, W. 
Nerpte No. 1. 
Polarity of No. of Time of 
Marked end. Readings. Observation. Temperature. Dip observed. 
Ss 16 6h. 43m., A.M. 76° Cho MATE 
N 16 woe Ut 4 TED 71° 33'.66 
Dip, by thirty-two observations on needle No.1, . . . . . . 71°89°.18 
Neepir No. 2. 
N 16 Th. 20m., A.M, 78° 71° 42'.43 
Ss 16 7 939 x 80 Wie a7 
Dip, by thirty-two observations on needle No.2, . . . . . . 71° 38'.56 
Dip, by sixty-four observations on needles Nos. land2, . . . . 71° 38'.87 
A RECAPITULATION, 
Showing the results of all the observations for the dip at the respective stations at Balti- 
more, on the 9th, 10th, and 11th of June, 1841. 
ist. At station three hundred and sixty-three yards N. 5° KE. of the Wash- 
ington Monument, by a mean of one hundred and twenty-eight observa- 
tions on needles Nos. 1 and 2, combined, June 9th and 10th, one 71° 47’ 24 
2d, At station S. 47° W., and distant one hundred and sixty-one feet from ihe 
curb-stone which marks the south-west corner of Calvert and Reed Streets, 
in the city plan, by a mean of sixty-four observations on needles No. 1 
and 2, combined, June 10th, 1841,. . . . . brett ee 
3d. At station 8.35 E., and two banited and bolita feet tesla station No. i, 
being forty-three feet north of line of iron pipes; by thirty-two observations 
two series, on needle No. 1, June 10th, 1841, . . . . 71° 48'.2 
4th. At station S. 8 E., and one hundred and eighty-one jest fon station 
No. 2, being one hundred and thirty-seven feet south of line of iron pipes, 
by sixteen obser vaviee On iecdic ING. 1, Janes), 1541,. .. . .. . 71° B0'% 
VOL. Ix.—93 
