18 REPORT OF THE SECRETARY. 



equator, as well as on her passage across the superior and inferior 

 meridian of the place. The moon produces high water at the same 

 instant of time on opposite sides of the earth, and were she constantly 

 to move in the plane of the equator, the highest points of these tides 

 would also be in the plane of the equator, and would consequently 

 produce a series of equal tides at any place either north or south of 

 this line. Bat it is evident that, when she ascends to the north, the 

 plane of the highest tide will tip in the same direction, giving the 

 highest point of one tide in the northern and the highest point of the 

 other tide in the southern hemisphere. Consequently, when the moon 

 has a northern declination, the tide at any place in the northern hem- 

 isphere which follows immediately after her passage across the me- 

 ridian will he higher than one which passes twelve hours later. This 

 variation in the height of the two tides is called the diurnal inequality. 

 From theoretical considerations it would not he anticipated that this 

 inequality should be well marked in such high northern regions ; but 

 since the movement of the water at Van Eensselaer's Harbor is not due 

 directly to the action of the sun and moon, but is the effect of an im- 

 mense wave propagated from the Atlantic through Baffin's Bay and 

 Smith's Straits, this inequality becomes well marked. 



About the time of the moon's maximum declination, the difference 

 between the day and night tide was two and a half feet. By an ex- 

 amination of the diagrams on which the elevations of the tides are 

 exhibited, it is seen that sometimes the day and sometimes the night 

 tides are the highest ; andj furthermore, that the difference vanishes a 

 day or two after the moon crosses the equator, and that it reaches its 

 maximum a few days after the moon attains its greatest declination 

 north or south. 



The form of the tide wave is also investigated and expressed in a 

 diagram, from which it appears that the spring tide wave is slightly 

 steeper between low and high w r ater than between high and low water, 

 or, in other words, that the water rises more rapidly than it falls, and 

 also that the neap-tide wave is nearly symmetrical, the rise and fall 

 taking place in nearly equal times. 



The tabulated observations were also investigated in reference to the 

 varying position of the sun and moon, giving rise to what is called 

 the half monthly inequality, and the result of this is also plainly in- 

 dicated by diagrams, for the high water as well as for the low. This 

 paper, as we have stated, completes the results of the discussions of 

 the series of observations made under the direction of Dr. Kane, and, 

 by themselves, or in connection with other researches in the Arctic. 



