and the motion of Auroral Beams. 41 



bridge on an average S^'SS earlier than at Toronto, and at Phil- 

 adelphia 1^-87 earlier than at Toronto. These results are a little 

 greater than those obtained from a comparison of all the obser- 

 vations, and indicate a motion somewhat more nearly east and 

 west ; but the general character of the results is the same. "We 

 seem authorized then to infer that in the eastern part of the United 

 Slates the irregular deflections of the magnetic needle, ichether attended 

 or not hy any auroral exhibition, are generally propagated in a di- 

 rection from K 68° E. to S. 68° W., and with an average velocity 

 of about 112 miles per minute. 



During the exhibition of brilliant auroras, auroral beams do 

 not ordinarily continue stationary for many minutes. They 

 generally exhibit a movement of translation towards the south, 

 and frequently also a movement to the east or west of the me- 

 ridian. In order to determine whether there is any uniform- 

 ity in the direction of this motion, I have collected together 

 all the notices of this kind which I could find recorded in the 

 Am. Journal of Science, in the Eeports of the K Y. Regents, 

 and in various other works. The following is the result of this 

 examination. 



Notices of lateral displacement of the auroral beams. 



Vol, xiv, p, 92, 1827, Aug. 28. New York City, Waves of light 

 began to flow from the eastern toward the western part of the luminous 

 arch. The whole arch moved towards the south. 



Vol. xiv, p. 94. Troy, N. Y. The flowing of the light from E, to W. 



Vol. xiv, p. 104. Canandaigua, N, Y. About the time that the arch 

 hroke up into columns, it seemed to move back towards the north. Soon 

 after it moved again to the south, apparently with a more rapid motion 



Vol. xiv, p. 105. 1827, Sept. 9. Canandaigua, N. Y. A light cloud, 

 moved gently to the west, and gradnally put on the appearance of beams 

 of light. Proceeding still west, and probably a little south, they seemed 

 to lengthen and descend toward the western horizon. The movement 

 westward was distinct, but not sufficiently so to enable me to estimate 

 the rate of motion. 



Vol. xiv, p. 106. lb. The western motion of the fragments was per- 

 ceptible, and was estimated at four degrees in thirty-two seconds. 



Vol.xxvii, p. 113. 1833, May 17. Philadelphia, Pa. This arch 

 Pa^^^ed gradually towards the south. 



. yol, xxvii, p, 119. 1833, July 10. Philadelphia. Four beams were 

 visible; the last beam vanishing after appearing to move westward. 



Vol.xxix, p. 389. 1835, Nov. 17. New Haven, Conn. The zone 

 nioved slowly to the south, until about 9 o'clock. From this time it be- 

 gan to recede northward. 

 ^M- JocR. Sci.-Sfxond Seeies, Vol. XXXIV, No. IOO.-Jult, 1883. 



