409 
2 76 sin (2 0 + 129°.) 
10£A, The usual method of taking monthly means gives only 
twelve points for the whole year, each point corresponding to the 
middle of a calendar month, the means being supposed to vary re- 
gularly from point to point. The author has combined two years’ 
observations for four places (Makerstoun, Trevandrum, Singapore, 
and Hobarton), so as to have four weekly means corresponding to 
each day in the year (Sundays excepted), and the most minute 
variations of these four weekly means for any one place are followed 
by those for the others. This fact is, however, only a corrollary to 
the following :■ — 
Daily Mean Variations. 
1HA, The daily mean horizontal force at all places on the surface 
of the globe increases simultaneously or diminishes simultaneously. 
The amount of increase or of diminution has generally the same 
value (the horizontal force at each place being the unit), so that 
the increase or diminution is in proportion to the absolute value of 
the horizontal intensity at the respective places. The variations 
from this result can be traced to disturbances which seem some- 
times to have a greater effect on the daily mean near the poles than 
near the equator. 
12iA, In order to follow the variations of the daily mean in 
shorter intervals than one day, the author has combined the obser- 
vations so that daily means are obtained corresponding for their 
middle points to each hour of the twenty-four, instead of to one 
hour only. This has been done for a period of six weeks only, in- 
cluding one of the 26-27 day periods (see 13iA) for the four places 
above mentioned (lOiA), and for Toronto and the Cape of Good 
Hope. The results are that the turning-points frequently agree to 
the same hour, though they also frequently differ to several hours ; 
the greatest variation being connected with large disturbances in high 
latitudes. Marked turning-points, maxima or minima at one place, 
are sometimes shown only as minor turning-points ; at others, and 
in the cases of some large disturbances, while the turning-point (say 
the commencing diminution of force) occurs at the same instant on 
all meridians, the rate or velocity of change is not the same in all — 
the rate probably depending on the hour of the day at which the 
disturbance has its maximum value at different places, the local 
