REPORT OF THE SECRETARY. 31 



appendix of the report for this year. Although the aurora is now 

 known to be an electrical phenomenon, it is certain that its region of 

 greatest activity is not the magnetic pole of the earth, but is in a 

 zone of several degrees in breadth, including the geographical poles 

 eccentrically; nevertheless, it is also clear that it is influenced in its 

 motions by the magnetism of the globe. 



The third part, which relates to tidal observations, consists of 

 two series : the first were made during November and December, 1 860 ; 

 the second in June and July, 186 L. In the first series the height of 

 the tide was noted every half hour; in the second series it was ob- 

 served at every ten minutes about the time of high and low water. 

 The apparatus employed consisted of a rope to which a stone was 

 attached at the lower end resting on the bottom and passing over a 

 pulley attached to a movable weight at the other. The pulley was 

 supported by a tripod standing over a hole in the ice at a short dis- 

 tance from the vessel, and the changes of the height of tide were 

 indicated by the vertical motion of the smaller weight. Corrections 

 were applied for the irregular stretching of the rope and also for the 

 errors of the watch. From the records thus corrected, Mr. Schott 

 has determined the height of the average sea level for each day, and 

 has compared this with the moon's declination parallax, or distance 

 from the earth, the atmospheric pressure, and the direction and force 

 of the wind. It is found that a variation of between one and two 

 inches in the height of the water is due to the changes in the moon's 

 declination from zero to its maximum value; also that a rise of one inch 

 in the mercury of the barometrical column is accompanied with a fall of 

 nearly four inches in the level of the sea. The effect of the wind, 

 though small, is apparent. With a northeast wind there was a de- 

 pression, and with a southwest an elevation, of the level; one proba- 

 bly blowing the water into and the other out of the strait. 



The general character of the tide at Port Foulke is similar to that 

 at Yan Rensselaer harbor, exhibiting two ebbs and two flows each 

 lunar day, with considerable diurnal variation, producing at Port 

 Foulke at certain times the character of a single daily tide — the two 

 waves as it were running into each other. The establishment, or, in 

 other words, the average lagging behind of the high water, after the 

 passage of the moon across the meridian of the place, is here half an 

 hour earlier than at Van Rensselaer harbor, which is distant 55 miles 

 in a northeast direction. This indicates a motion in accordance with 

 the general direction of the tidal wave, which in this region is not 

 due to the direct attraction of the moon, but is derived from the 

 great tidal wave of the Atlantic ocean. 



