268 



Magnetic Observations. 



In the diagram the central circle is the brown-stone monument of 

 the magnetic station; the other circles near this central station are 

 the limestone piers of the astronomical instruments. 



The geodetic coordinates of the brownstone monument are 

 Latitude = 42° 39' 43". 63. 

 Longitude, in arc = 73° 46' 33".48. 



" in time = 4h. 55m. 06.23s. W. from Greenwich. 

 Altitude = 227 fiftfath feet above mean tide level. 



While there are several phases of the magnetic phenomena, usually 

 investigated at permanent stations; as the intensity with which it 

 affects magnetic matter, the dip angle and perturbations of these 

 phases of its force, yet the "variation" or, more properly, the Declina- 

 tion of the magnetic needle has been chiefly studied by navigators 

 and surveyors, as of immediate practical importance, and hence 

 their records afford the most ancient data, and the best basis for 

 magnetic investigations. When the intensity and dip have been fully 

 correlated mathematically to the declination, we may be able to hope 

 for a full knowledge of the general magnetic influence by means of 

 observations of the declination alone. 



The declination of the magnetic needle is to us, therefore, the most 

 important reaction of the magnetic force upon matter; and it is for 

 this reason, that I have specially studied, and made it the subject of 

 the present paper. 



I here, therefore, present in tabular form : 



(1.) A collection of observations of the magnetic declination at 

 Albany, N. Y. 



(2.) A table showing prediction computations, which I have made 

 by the mathematical formula hitherto regarded as the expression most 

 conveniently representing the declination, according to the idea en- 

 tertained by mathematicians, of the local magnetic law at Albany. 



The formula, by which the results in table second were computed, 

 was devised by Prof. Charles A. Schott, chief of the computing 

 division of the U. S. Coast and Geodetic Survey at Washington. This 

 formula he calls empirical. It was prepared many years since on tne 

 basis of the few observations then available for this locality. 



The newly collected and observed data presented in this paper ex- 

 tends more than one hundred years back of the data which Prof. 

 Schott used as the basis of his formula; and, doubtless, on this new 

 data a more exact formula may be constructed. 



