17G 



A Specimen of Sponge, and Nineteen Specimens of Shells, from Cen- 

 tral America. — From the same. 



Prof. Bache read a paper, entitled " Observations of the 

 Magnetic Dip in the United States, Fourth Series, by Elias 

 Loomis, Professor of Mathematics and Natural Philosophy in 

 Western Reserve College, Ohio," which was referred to a 

 Committee. 



Professor Loomis begins this paper by giving the results of further 

 experiments to test the accuracy of the axle of his dipping needle, 

 namely, a series made by Mayer's method; these proved satisfactory, 

 the individual results presenting some discrepancies, but the mean 

 agreeing very nearly with the dip previously obtained. The mean of 

 observations hitherto made with this needle by the usual method, and 

 by the series in different azimuths and by Mayer's method combined, 

 differed but 0.1', correction having been made to reduce the observa- 

 tions to the same epoch. 



Prof. Loomis then gives the magnetic dip observed by the ordinary 

 method at the following named places, as follows: 



Brooklyn, Ohio, April 23, 1841, lat. 41° 30' N., long. 81° 43' W., 

 Dip 73° 16'.3. 



Tallmadge, Ohio, April 26, lat. 41° 06' N., long. 81° 27' W., 

 Dip 72° 55'.2. 



Tallmadge, Ohio, Oct. 13, lat. 41° 06' N., long. 81° 27' W., 

 Dip 72° 51 '.5. 



Cleveland, Ohio, August 12, lat. 41° 30' N., long. 81° 41' W., 

 Dip 73° 04'.3. 



Monroe, Michigan, Aug. 14, lat. 41° 55' N., long. 82° 28' W., 

 Dip 73° 19'.0. 



Ypsilanti, Michigan, August 16, lat. 42° 14' N-, long 83° 38' W., 

 Dip 73° 18'. 8. 



Ann Arbor, Michigan, Aug. 16, lat. 42° 18' N., long. 83° 45' W., 

 Dip 73° 16'.5. 



Detroit, Michigan, Aug, 17, lat. 42° 19' N., long. 83° 03' W., 

 Dip (mean of four series at three stations) 73° 35'. 3. 



Mackinac, Michigan, Aug. 21, lat. 45° 51' N., long. 84° 41' W., 

 Dip (mean of four series at two stations) 76° 38'. 9. 



Fort Brady, Michigan, Aug. 25 & 27, lat. 46° 30' N., long. 84° 

 24' W., Dip (mean of three series at three stations) 77° 29'.7. 



Gros Cap, Canada, Aug. 26, lat. 46° 32' N., long. 84° 43' W., 

 Dip 77° 05'.3. 



