142 ABSTRACTS FOR THE HoriIzoNTAL FORCE. 
TABLE X.—continued. 
Mean of the || Range from the 
Four Hours. Four Hours. 
1842. Se. Div. 
July 517-81 
August : 518-15 
September 520-56 
October 525-62 
November 528-65 
December 533-15 
In Tables VIII. and IX. the mean of the four observations has been given as an approximate mean for each 
month ; the last column contains the range deduced from these four observations, and is probably not far from the 
true diurnal range. 
In all the months, with the exceptions of January and December 1842, 23" shews the least force of the four 
hours ; the greatest force is at 5%. In January and December 1842, the greatest force is at 2"; in October 1842, 
and November 1841 and 1842, the force at 2" differs little from that at 5". The minimum seems therefore to 
occur throughout the year a little before 23" (or before 10" a, m. Makerstoun mean time) ; the maximum about 5" 
(or 44 p.m. Makerstoun time) in summer, and between 2" and 5 (or 1" and 4% p. mw. Makerstoun time) in winter. 
In December 1842, the maximum occurs about 2" p.m. Makerstoun time. The diurnal ranges, as given in the 
last column, though affected by the shifting of the curve in the summer and winter months, shew markedly a great 
and regular increase from winter to summer, and decrease from summer to winter. Although the rejection of the 
days of irregularity have considerably softened the asperities in the Means of Table VIII., the depressions in June 
and July being considerably removed when compared with May, the depression in April still remains. 
The force on the whole increases from the beginning of the year till the end; the increase being most rapid 
after September 1842 ; and it is nearly constant for the summer months. 
The following Table has been deduced from Table X. 
TABLE XI.—The Means of the Bifilar Magnetometer Readings minus the least mean, in parts of the whole 
Horizontal Force, for periods of Three Months, for the Summer and Winter Months of 1842, and for the 
Year 1842. 
Period. 20%, : 2h, 5h, Range. 
1841. 
July, Aug., Sept. 0-00058 0-00000 0-00177 0-00288 0-00288 
Oct., Nov. 0-00046 0-90000 0-00071 0-00112 0-00057 0:00112 
1842. 
Jan., Feb., March 0-00256 0-00210 0-00312 0:00349 0-00282 0-00139 
April, May, June 0-00279 0-00220 0-00378 0-00480 0-00339 0-00260 
July, Aug., Sept. 0-00329 0.00257 0-00440 0-00509 0-00384 0-00251 
Oct., Nov., Dee. 0-00502 0-00462 0-00540 0-00547 0-00513 0-00085 
Jan., Feb., March 5 
Oct., Nov., iD % \ 0-00379 0:00336 0:00426 0-00448 0-:00397 0-00112 
0-00304 0:00238 0-00409 0-00494 0-:00361 0-00256 
April, May, June, 
July, Aug., Sept. 
The Year 0-00341 0-00287 0-00417 0-00471 0.00379 0-00184 
The quarter, July, August, and September, is not comparable with the following period. 
The Means for 1842 shew a regular increase of force in the first three quarters ; in the last the force increases 
with more rapidity. 
