72 



DISCUSSION OF THE I N F 



I ; X ( ' I ■: ( ) F T BE M<><> X 



(A.) — LOKAK-DlDKXAL VaRIATI 



+1.5 



the Horizontal Force in Sdmmer and Winter. 



n < 1 1 1 1 — i r~ 



0" 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 18 17 18 19 20 21 22 23 24" 

 U. C. (Western hour angles of the moon.) L. C. (Eastern hour angles of the moon.) D. C. 



summer deflection. 



winter deflection. 



If there is any marked difference in the lunar diurnal variation in the summer 

 and winter season, the summer range is slightly greater than the winter range; as 

 to the epoch, there is no douht that in winter the lunar maxima and minima arc 

 earlier than in summer. It is a remarkable fact that we have found the same fea- 

 tures in the lunar effect on the declination, viz., a greater amplitude in summer and 

 an earlier occurrence of the maxima and minima in winter; the amount of the 

 shifting of the two curves appears to be nearly the same. From the ten year series 

 of observations at Prague (1840-49) Mr. Karl Kreil found a larger lunar effect in 

 the summer months than in the winter months. 



Recurring to the final values of the lunar-diurnal variation of the horizontal force. 

 as given in Table VIII., they can be represented 1>\ the usual Besselian form of 

 periodic functions. 



The angle counts from the moon's upper culmination westward at the rate oi 

 15° to an hour; a + sign indicated greater, a — sign, less force than the average 

 normal. The observed values are represented by the following expression: — 

 ,/ c = _ o.oi + 0.40 sin (0 + 13° 29') + 0.60 sin (2 + W° 43') + 0.155 sin (3 



+ -2ii° 31'). 

 The three coefficients arc expressed in scale divisions; if expressed in parts of die 

 horizontal force the equation maj be written as follows: (.1/ signifies millionth parts 

 of the force.) 



.)/ M M .1/ 



// c = _().36 h 1 l.iio sin ( ' I 13 .5) + 21.90 sin (2 6 + 3K r .7) + 5.64 sin (3 6 + 



24 I .5.) 

 If expressed in absolute measure and if n = number of hours after the upper cul- 

 mination, it may be written 



.1/ ' .1/ M M 



ff € = _ 1.5 + 61.0 sin (15 n 4- 13°.5) + 91.5 sin (30 n 4- 39°) + 23.6 in I I > n 4- 



244°.5.) 



