HORIZONTAL FORCE OF THE EARTH’S MAGNETISM. 
403 
results (see Table V.). Noting that the greatest latitudes are between 5 o, 0 and 5°-3, we 
find 
° . ° 
13 cases, mean latitude beginning 3 6 S., ending 4'G S. 
8 „ „ „ 4-6 N., „ 4-5 N. 
1 case „ „ 3-4 N., „ 2-4 N. 
6 cases beginning and ending within the limits 3'0 S. and 3 O- 0 N. 
There were 21 cases for each of which the moon’s mean latitude was greater than 
3° S. or than 3° - 3 N. ; 1 case for which the mean latitude was 2 0, 9 N. ; and 6 cases for 
which the mean latitudes were between 1 0, 7 S. and 0°*8 N. The relative amounts of the 
diminutions of magnetic force are projected on curves supposed to represent the moon’s 
path in declination (fig. A) and in latitude (fig. B, Plate 38). 
It will be seen from these two figures that 13 cases occurred for the moon when 
passing from the greatest northerly declination towards the equator, while for the 
passage below the ecliptic there were 16 cases. From near the greatest southerly 
latitude (fig. B) to near the greatest northerly latitude (embracing 11 days of the whole 
period) there were only 2 cases. The proportion of cases for the two portions of the 
moon’s path was as 26 : 2, whereas the ratio should have been as 16 : 12 had the chances 
of disturbance been equal for all parts of the moon’s orbit. 
There is no doubt, then, that in 1844 and 1845 the greater disturbances of mean mag- 
netic force occurred most rarely when the moon was near the equator or ecliptic ; but it 
is not possible to determine from two years’ observation whether the moon’s action 
depends on her position relatively to the one or the other plane only, or to both. If 
the thing acted on, whatever that may be, retains the same position relatively to these 
planes, the discussion of 5 or 6 years’ observations will show to which plane these results 
should be referred. 
The preceding investigation was limited to cases for which the diminution of daily 
mean horizontal force within three days was not less than one thousandth of its whole 
value ; the change of daily mean horizontal force from day to day (without regard to 
sign or limit) has also been sought for- the solar and each of the lunar periods. The 
results confirm the conclusions already derived from the greater negative movements, as 
to the solar meridians and moon’s latitudes for which the disturbance is a maximum. 
I shall defer, however, the consideration of this part of the investigation till a longer 
series of observations has been discussed. 
