MAGNETIC DECLINATION AND HORIZONTAL FORCE. 
19 
sion of the phenomena in question, there is nothing anomalous in our finding, as we 
do in fact, definite lunar diurnal variations from the observations of complete lunations. 
It will, indeed, be seen further on (paragraph 17) that the lunar half-day wave is one 
of the two most prominent, and that the lunar day wave has, generally speaking, an 
amplitude as great as any of the remaining five. 
14. Proceeding now to find the values of having entered the observed 
lunar diurnal variation for new moon in a Table having the solar hours, from 0 to 23, 
marked at the top of the columns, commencing with 0 hours of the lunar day, we 
enter underneath this the observed lunar diurnal variation for full moon, commencing 
with 12 hours, and then subtract the lower entries from the upper: half the 
difference we take to be the value of f c .i{h) as derived from the new moon and full 
moon variations. Similarly, entering the observed lunar diurnal variation for first 
quarter, commencing with 18 hours, and under it the observed lunar diurnal variation 
for last quarter, commencing with G hours, and subtracting the lower numbers and 
dividing by 2, we obtain the value of f,.i(h ) as derived from the first quarter 
and last quarter variations. In like manner we obtain from the observed lunar 
diurnal variation for the one-eighth and five-eighths phases the value of 
f c .i(h ) cos 45 Cj rf s .i(h) sin 45° or i(A)} =ct (say); and from the variations for 
the three-eighths and seven-eighths phases the value of fc.i(h)-\~fg.i(h)} = ?>(say): 
combining the last two quantities, we find ^ ) = fc.\ and ~^(a-\-b) =f s .i as values 
derived from the variations of the eighths phases. In Tables 11 to 18 are collected 
together the results of these various calculations. 
