Magnetic Observations. 



I had hoped at this time to present a new formula of my own com- 

 putation for this local magnetic law on the basis of the new data; but, 

 as the time at my disposal has not been sufficient to permit me to as- 

 sign weights (or estimates of precision) to each of the observations 

 communicated, I must defer the pleasure of presenting this new formula 

 until another time; and will merely transmit my observations and col- 

 lated data, accompanied by computations by the old formula; which, 

 while affording a scale of numerical comparison with the observations, 

 will serve some present purposes, and give an idea of the supposed ex- 

 tent of the secular change in declination and of the processes, so 

 far, devised for the prediction of the phenomena. 



Using the old data only, the empirical formula of Schott for the 

 magnetic declination at Albany is — 



D = + 8°. 17 + 3°-02 Sin (1-44 m — 8°. 3) 

 in which D=the declination at any desired time in calendar years 

 from the epoch 1850. 



From this formula it will be seen that the terrestrial magnetic force 

 is not as simple a form of energy as gravitation; especially in view of 

 the fact that this is only one expression, suited to only one locality, 

 and not applicable to any even moderately distant place. 



This shows how important is the annual collection of local magnetic 

 data, at a great number of points, if we are ever to attain a better 

 understanding of the nature and origin of the magnetic force. 



The computations in table (2) by the old formula I have extended 

 beyond the limits for which they were probably intended in order to 

 show the maximum and minimun points and numerical nature of the 

 curve of declination according to Schott's formula, as well as to com- 

 pare its values with the actual observations newly communicated in- 

 the first table. In this table the last column shows the ± differences 

 of the results by fornmla from the actual observations. 



With this explanation, this collection of data is herewith transmitted 

 to the Institute, with the hope and intention that in a future paper 

 these results will be discussed and some advancement made in the local 

 theory and formula for the prediction of magnetic phenomena at 



