148 



to the diminution of dip in the interval. Professor Bache stated that 

 it was so desirable that each succeeding observer in a given place 

 should, when a well selected site had been employed for observations, 

 use the same, that he had only left the position used by Professor 

 Henry on account of changes which had been made by putting up an 

 iron railing about the Park. In the case of the two series by Pro- 

 fessor Loomis, and by Professor Courtenay and himself, the stations 

 did not appear to have been generally in common. 



Professor Bache further observed that the diminution of dip at New 

 York, according to his observations, compared with those of Major 

 Sabine, had been at the rate of nine minutes in twelve years, between 

 1822 and 1835; while those of Professor Loomis would give but eight 

 minutes in seventeen years. Both results are probably too small. 



Professor Bache concluded by stating, that the general tenor of the 

 comparison between these two series of observations, indicates that the 

 relative correction for the two pairs of needles was subtractive for 

 those of Professor Loomis, and additive for those which he had used ; 

 but that as they had been furnished by the same maker, and were of 

 similar dimensions, there was, until they had been compared with 

 other needles, no just ground of preference for either. 



The following resolutions in relation to combined magnetic 

 observations were adopted: 



Resolved, That in the opinion of the American Philosophical So- 

 ciety, it is highly desirable that the combined series of magnetic ob- 

 servations now in progress under the direction of the British govern- 

 ment, should be extended to the United States, by the establishment 

 of Magnetic Observatories at suitable places. 



Resolved, That a Committee be appointed, with authority, on be- 

 half of the Society, to invite the attention of one of the departments 

 of the Government of the United States to the plan for combined 

 magnetic observations, a sketch of which was presented in the docu- 

 ments from a Committee of the Royal Society of London, and to urge 

 co-operation in the plan as a national undertaking, in every way 

 worthy of the United States. 



The Committee under the above resolution, consists of Pro- 

 fessor Bache, Doctor Patterson, Professor Henry, Mr. Kane, 

 and Colonel Totten. 



Professor Bache, reporter, stated that No. 8 of the Proceed- 



