Burhank — Apparent Variations of the Vertical. 329 



appearance of the record if the sun shone for a couple of hours 

 during the day. No definite tilting could be observed on the 

 N-S component. This may be due in part to the fact that the 

 absolute observatory is placed directly south of the variation 

 observatory, thus shading the ground on that side. 



In fig. 3 are shown a few curves of the E-W component 

 from the records of the year 1906. The lowest curve is for 



Fig. 3. 



the N-S component and shows the inappreciable amount of 

 tilting it experienced. 



Of the eleven days for which curves are given, Feb. 21 was 

 cloudy, Aug. 20 and 21 partly cloudy, and all others were clear. 



In these curves a negative ordinate or motion downward 

 indicates a movement of the top of the W-E pier toward the 

 east and of the N-S pier toward the north ; movements up- 

 ward corresponding to tilting toward the west and south. 



Am. Jour. Sci. — Fourth Series, Vol. XXX, No. 179.— November, 1910. 



