VERTICAL COMPONENT OF MAGNETIC Forct. 245 
winter than in summer, as there is an indication of a minimum about 5" a.m. The following are the results 
from the mean of both years :— 
The principal minimum at 1" 10™ a.m., Makerstoun mean time. 
The principal maximum at 6" P.M., se 
A secondary maximum at 95 10™ a.m., 
A secondary minimum at 11? 40™ a.m., 
The same results may be deduced from these means as have been already deduced from the means 
Table XVIII. 
SECULAR CHANGE OF THE VERTICAL COMPONENT OF MAGNETIC FORCE. 
The means for the year 1844 shew that the means of the observations at 22 and 0", and at 4" and 64, 
are respectively very nearly the same as the means of the observations at 23" and 5", Assuming that they 
are equal for the year 1843, we shall have from the means for the year at the foot of Table XVIII. = 0:000100 
and from the mean for the year deduced from the means at the the foot of Table XV. = 0:015935. 
Mean at 20" less than the mean of 9 observations from Table XVIII. by 0-000040, or = 0-015895 
Mean for 23" ............ tesecsensersseeees 0°0000839, or = 0-015896 
AV siraigen ta Lanes 2 Oe ate a Nett eRe eR EM Eee neni Tao ASP eis east 2a daisas sone ge besigns 0:000044, or = 0:015891 
PAD Oy Wye T CALC again MAMET ode Nagecs be s-EeeGscratscwacpecsscseonss 0-000078, or = 0:016013 
From Table XVII., Abstracts for the observations of 1842, we have the means in micrometer divisions at 
the corresponding hours in 1842, these being converted into parts of force by the first formula given in the 
remarks to Table XV. we have, 
1842 ; 20" = 0-017902, 23" = 0-017962, 2 = 0:017980, 5" = 0-018147. 
The means above for 1843 being subtracted from these, we have— 
Secular change, 20"= —0:002007, 23= —0-002066, 2= — 0-002089, 5"= —0-002134. 
Mean secular change 1842 to 1848, = —0:002074. 
RANGES OF THE MonTHLY MEANS OF THE DIURNAL VARIATIONS. 
The ranges given in the last column of Table XVIII. must be very imperfect for some months, since the 
minimum actually occurs in general a little after midnight. It is very obvious, however, that the range is 
greatest at the equinoxes, and that it differs little in summer from winter, thus the diurnal range of the mean 
for the winter group of months is 0:000204, for the summer group 0°000222, while for the group at the 
equinoxes it is 0:000317. The corresponding groups in Table XIX. give the following ranges :— 
Diurnal range; winter group = 0-000251 ; summer group = 0:000492; equinoctial group = 0:000788 ; 
or nearly in the ratios of 1, 2, and 3. 
TABLE XX.—Diurnal Ranges of the Vertical Component of Magnetic Force, as deduced from the 
9 Daily Observations in 1848, with the Weekly and Monthly Means. 
MAG. AND MET. oBs. 1843. 
January. | February. March, April. May. June. July. August. |September. October. |November.| December. 
0-00 0-00 0-00 0-00 0-00 0-00 0-00 0-00 0-00 0-00 
[see ] 0227 0130 0226 0168 0292 0492 O211 | es [0481] 0400 
0959 0099 0111 [0865] 0258 0414 [0363] 0297 | verses 0421 0468 
0356 0159 0135 0371 | 0314 0597 0406 0366 [etree ] 0501 [0270] 
0056 0162 0474 0332 0338 0405] 0185 1536 | seeeee 0282 0184 
0096 [0283] | [0810] 3738 0200 0469 0238 0288 | ses 1011 0286 
0251 0802 0434 0373 2713 0264 0274 [0798] 0262 0396 0166 
0267 0355 3300 1416 [0894] 0398 0300 0266 0436 0228 0247 
[0360] 0123 0407 1330 0512 0421 0945 0807 0459 [0341] 1177 
0610 0280 0322 [0838] 1010 0139 [0361] 1526 0542 0139 0555 
0259 0165 0191 0363 0590 0254 0378 0353 [0459] 0133 [0633] 
0676 0276 0163 0434 0185 [0387] 0140 0399 0418 0141 0822 
[0351] | [0347] 0499 0143 0552 
