REPORT OF THE SECRETARY. 27 



General kSabine in his reduction of the results of the British observa- 

 tions. The records, after having been corrected for the influence of 

 the sun and other perturbations, were arranged in tables, correspond- 

 ing to the several hours of the day, commencing with the upper transit 

 of the moon over the meridian. To ascertain whether the different 

 parts of these series would give harmonious results, the whole number- 

 tabulated, 21,644, was divided into three groups, the first compris- 

 ing nineteen months, the second, twenty-one months, and the third, 

 eighteen months. From these it was found that the results were 

 nearly proportioned to the number of observations, which indicated 

 that no constant error of much magnitude existed. 



The three groups were next discussed by means of Bessel's formula, 

 two terms of which were found sufficient to give a curve representing 

 the observations ; and as a constant term was not found necessary in 

 the construction of this curve, it was inferred that the moon exerted 

 no specific constant action on the needle, or, in other words, that the 

 magnetism of the moon is not per se, but is of that kind called 

 inductive, which is due to the action of some extraneous body. ' 



The curves by which the results of the discussion are represented 

 show two east and two west deflections in a lunar day, the maxima 

 east and west occurring about the time of the upper and lower transit 

 of the moon over the meridian, and the minima about at the interme- 

 diate sixth hour. 



In comparison with the effects of other forces operating on the mag- 

 netic needle, that of the moon is exceedingly small, and could not have 

 been detected previous to the introduction of the more refined instru- 

 ments and methods of investigation which have been invented within 

 the last twenty years. The total range at Philadelphia scarely reaches 

 thirty seconds, and at Toronto it is only a little more than thirty-eight 

 seconds. 



The principal western maximum deviation occurs six minutes after 

 the moon passes the lower meridian, and amounts to 13.8 seconds of 

 arc. The secondary maximum occurs fourteen minutes after the upper 

 culmination, and amounts to 10.8 seconds. The principal eastern 

 maximum of variation takes place six hours and seventeen minutes 

 after the lower culmination, the deflection being 13.2 seconds. The 

 secondary easterly maximum occurs at six hours three minutes after 

 the upper transit, and amounts to 11.4 seconds. 



The effect of the moon appears to be subject to a variation depending 

 on the solar year, for the investigation of which the preceding results 

 were arranged in two groups — one containing the hourly values for 



