10 



OBSERVATIONS ON 



were mounted under a tent, with all necessary precautions of removing every iron 

 or steel article, and adjusted sufficiently early in the day to begin with the maxi- 

 mum or eastern declination, and continue the readings, at least as often as every 

 half hour, say from 8 A. M. until the minimum or extreme western reading in the 

 afternoon about 2 P. M. Finally, after making the proper equations for the error 

 of the theodolite, and for that of the zero of the scale of the collimator, the mean 

 of the declination for the day has been tabulated as in the following paper. The 

 azimuths, and, of course, the true meridian to which these declinations have been 

 referred, are, in most cases, those of the Coast Survey, determined by iutervisible 

 stations, and accurate within ten seconds of space. In some few cases, where such 

 azimuths could njot be obtained, the meridian was determined by altitudes and 

 azimuths of the sun, observed at the time by means of the theodolite. 



The intensity of magnetic force has been determined, as heretofore, by oscUlating 

 three Hansteenian needles in the exhausted receiver invented by Prof. Bache. As 

 my dip-needles were gone at the time, I could not make my usual comparative 

 observations at Cincinnati, including the element of the dip. 



Under these circumstances, I have compared the following series with Cincinnati, 

 through observations previously made- at Mrs. Morris's garden, at Washington 

 Place, in Newark, N. J. By means of the observations made there in April 29, 

 1844, the dip at Cincinnati was calculated to be 70° 24', which, although less by 

 from 1' to 3' than has been usually observed, has still been found to be consistent 

 with the observations previously made at Bloomingdale Asylum and at Girard 

 College. 



Tabttlated Results of Seeies IX. 



Dip. 





Epoch of 

 commencing 

 "vibration, 

 hrs. min. sec. 



Duration 

 of 500 

 Tibra- 

 tions. 





Calculated 

 duration 

 at 60°. 



Square of the 

 preceding. 



Horizon- 

 tal inten- 

 sity. 



Total in- 

 tensity : 

 hor. be- 

 ing 1000. 



Total inten- 

 sity : that at 

 Cincinnati 

 = 1000. 



158. Pinley's Station, about 10 miles from Baltimore. — Lat. — ° — ' — " N. Long. — ° — ' 

 W. April 13, 1846. 



71° 46' 50" 

 Var. 2 19 30 W. 



4 

 5 

 6 



11 27 01.2 A 

 10 44 01.2 

 9 40 04.4 



1157.6 

 1406.8 

 1401.2 



50.25 

 49.00 

 48.00 



1158.37 

 1407.88 

 1402.68 



13418210569 



19821260944 



19675111824 



Mean 



914.05 

 917.50 

 918.50 

 916.69 



2931.96 



983.00 



159. Bloomingdale Asylum, N. Y.— Lat. 40° 49'? N. Long. — ° — ' W. April 27, 1846. 



72° 38' 17" 

 Var. 5 12 27 W. 



4 

 5 

 6 



10 46 01.2 A 



11 18 59.8 



12 47 00.2 P 



1183.4 

 1436.0 

 1430.8 



66.00 

 66.50 

 68.50 



1182.94 

 1435.45 

 1429.73 



13993470436 



20605167025 



20441278729 



Mean 



880.67 

 882.60 

 884.08 

 882.45 



2957.20 



992.00 



REMAKES. 



158. Finley's Station. — Geology primitive. Soil abounding with metamorphic small bowlders and 

 pebbles, white, yellow, and brown, apparently not magnetic. 



159. Bloomingdale Asylum, N. Y. — Geology primitive; prismatic gneiss rock, underlaying the soil, 

 some trappean bowlders, but none near the instruments. 



