Proceedings of Scientific Societies. 375 



N. S.,) and to that of Prof. Courtenay and himself The discrepancies 

 at Philadelphia and Baltimore were among the most striking. Having 

 satisfied himself that the dip given by his instrument at the station occu- 

 pied by Prof Loomis, near Philadelphia, was sensibly the same as that 

 given by Prof Loomis, his next step was to ascertain, by observations in 

 a different position from those used in both the sets of observations form- 

 erly made, which probably represented more correctly the dip at Phila- 

 delphia. The result of two series of observations near the observatory at 

 the Girard College, (at a sufficient distance to be beyond sensible influ- 

 ence from the magnetic instruments,) made with four different needles, 

 was as follows : — 



July 21, 1840. No. 1, 71° 51.7'. No. 2, 71° 51.7'. Mean of Lloyd, 

 No. 1 and No. 3, 71° 55.8'. 



November 2, 1840. No. 1, 71° 51.2'. No. 2, 71° 51.0'. Mean of 

 Lloyd, No. 1 and No. 3, 71° 57.4'. 



Mean, 71° 53.3'. 



The needles, termed Lloyd No. 1 and No. 3, are used without rever- 

 sing the poles ; and a correction has been applied from the mean of six- 

 teen comparisons, with the ordinary needles, at different places : as, 

 however, this correction is obtained through Nos. 1 and 2, the results 

 merely add to the number of observations from which the mean is ob- 

 tained. 



Prof Bache remarked that his former result was thus confirmed. 



At Baltimore, the place of observation was in the second square, N. E. 

 of the Washington Monument. The same needles were used. 



Aug. 27, 1840. No. 1, 71° 31.7'. No. 2, 71° 39.1'. Mean of Lloyd, 

 No. 1 and No. 3, 71° 32.4'. Mean, 71° 34.4', differing from the results 

 of both the former series. 



Prof Bache stated, in continuation, that the geological formations at 

 and near Baltimore, rendered it difficult to select an unexceptionable site 

 for magnetic observations there, and was a sufficient explanation of the 

 observed discrepancies. The results, which he had at present obtained, 

 differed about 10' from the mean of those of Professors Courtenay and 

 Loomis. 



Dr. Patterson announced the death of Prof Charles Bonnycastle, a 

 member of this society, (elected at the last meeting,) which took place on 

 the 3 1st of October. 



Nov. 20. — Dr. Patterson, from the observatory committee, reported, 

 that an ordinance had passed the city councils, authorizing the erection of 

 an astronomical observatory within Rittenhouse square. It was subse- 

 quently resolved, that the terms of the ordinance be accepted by the so- 

 ciety, and that the observatory committee be instructed to take the neces- 

 sary measures under the powers given them, for carrying into eifect the 

 objects of the ordinance. 



