32 



APPENDIX. 



The action on the declination magnet appears to be that of alternate deflections either way from 

 the normal position; in 5 cases the deflection was west, in 2 cases east, more frequently there were 

 one or two successions of west and east deflections (or the reverse) in one instance even three ; these 

 alternate excursions appear to be a characteristic sign. In 5 cases the tendency of the deflection was 

 easterly, in 6 cases westerly, and in the remaining 8 cases in both directions. The average amount 

 of deflection is 17'. With but one exception the uniform effect upon the horizontal force was to 

 decrease it. In the exceptional case a decrease followed the increase ; in another case the reverse 

 took place ; during one aurora there was at first a fall in the force, then a rise, and again a fall. The 

 average depression of the horizontal force below the normal value was 0.005 parts of the force (0.021 

 in absolute measure). The effect upon the vertical force is small ; in 9 cases no disturbance occurred ; 

 in general the force is less than the normal; there are two exceptions to this in the 13 cases. The 

 average depression of the vertical force below its normal was 0.0007 parts of the force (0.009 in abso- 

 lute measure), or irrespective of sign 0.0013 parts of the force. If we wish to compare the tabular 

 differences in declination and horizontal and vertical force with the magnitude of the recognized 

 disturbances, the latter are 4' and 0.001 (parts of the force) for either the horizontal or vertical 

 component. 



Of the auroras noted, that of May 29, 1840, was in many respects the most remarkable, and the best 

 observed both as to its appearance and as to its magnetic effect ; its study can be recommended to 

 those who have occasion to test their theoretical views in reference to this phenomenon, and to ter- 

 restrial magnetism. Its appearance at New Haven, Conn., has been described by E. C. Herrick 

 (Sill. Jour., 1840, Vol. XXXIX, p. 194). It was seen over a great portion of the United States, in 

 Canada, and England. See, also, description in the volume of the Toronto Observations; also an 

 extract from the proceedings of the British Association (Sill. Jour. Vol. XL, p. 337) ; also (p. 338 

 ibid.) note on the same by the Astronomer Royal. 



The total number of auroras which occurred at Philadelphia was much greater than the number given 

 above, as has already been stated. At Toronto the annual distribution of the phenomenon over the 

 same period of time, and for three years beyond the close of the record at Philadelphia, is as follows : 

 In 1840 (from March) on 23 nights. 



1841 

 1842 

 1843 

 1844 

 1845 

 1846 

 1847 

 1848 



36 

 14 

 16 

 20 

 19 

 27 

 29 

 66 



