89 
units of resistance ; so that we have there a tide-producing 
force due to the resistance alone and equal in amount to 
the difference between that resistance and the amount of 
the lunar attraction. 
A very little reflection will suffice to show that in what- 
ever part of the earth’s figure the common centre of gravity 
of the system may be found, the tide-producing energy result- 
ing from the forces here named will be substantially the 
same on both sides of the earth. For instance, if we regard 
the figures representing the earth’s diameter, the moon’s 
distance, and the mass of both bodies, as being correctly 
given in the tenth edition of Herschel’s “Outlines,” we 
shall find the centre of gravity of the system to be 1249 
miles below the surface of the earth. Here we have no 
centrifugal force at all, but at a distance beyond of 2713 
miles (i.e. at the centre of the earth) we have one lunar unit 
and no more. Under the moon, where the attraction is 
1’034 lunar units, the augmenting centrifugal force is ’46 of 
a lunar unit, and the tide-producing force equal to the 
amount of their sum, or 1'494 times the same standard of 
measure. On the further side of the earth, however, the 
centrifugal force equals 2 “46 times the amount experienced 
at the centre, whilst the attraction of the moon at the same 
place is “968 of that amount. The difference of these forces 
or 1“492 lunar units indicates the comparative amount of 
force available for raising the external terrestrial tide. 
“ Rainfall at Old Trafford, Manchester, in the year 1873,” 
by G. V. Yernon, F.RA.S., F.M.S. 
The rainfall of 1873 was 5“950 inches below the average 
of the last 80 years, and no less than 21*877 inches below 
the great fall of 1872. 
The total fall in 1873 was 29*815 inches, and fell upon 
198 days; although the fall was below the average it fell 
upon an unusual number of days, and was 6 days above the 
average of the last twelve years. 
