318 



REPORT 1893. 



chance for studying the effects of the tides than the Bristol Channel, with 

 its enormous variations of the water-level. 



The following formula expresses, in the same unit as above, the ordi- 

 nary lunar deflection of the plumb-line ; and it will be remarked that the 

 latter is very small compared with the observed deflections : — 



50 sin 22 cos (^-270°)-f37 cos^ S cos (2^-270°), 



where 8 is the moon's declination. 



As it might be of interest to the reader to be able to judge for himself 

 how far the formula for Wilhelmshaven represents the observations, I 

 have appended the following table of the values of the coefiicients a^, fej, 

 and 0.4, &4.' a^, &2 were given above, and the changes in a^, 63 are less 

 pronounced, this term being altogether the smallest. The unit is again 

 0""0028, and each pair of constants rests on about twenty days of 

 observations. 



II. The Daily Oscillation and its Changes- — The most prominent feature 

 in the curves is a daily oscillation, which, from the agreement between the 

 observations taken at three different places under varied conditions, must 

 be considered as a phenomenon of a universal, and not of a local, cha- 

 racter. 



If we take the means of all the observations the daily motion of the 

 horizontal pendulum, which, when it is placed in the meridian, repre- 

 sents the east- west component of the motion of an ordinary pendulum, is 

 described in the following table : — 



' Tlaese values refer to Greenwich mean time, whilst in the formula t has been 

 redaced to local time. 



