580 MR J. A. BROUN ON THE 


Place. Observer. Years. Ranges, : Ratios. Observations. 
Munich, Lamont ; ae == C—O 2 8 am.tol P.M. 
4 4 i prlerdis F baee = 167 { 7 am.tol pm.— 
1856°5 7:08 8 am. to2 P.M. 
» » ; rare 5 =o = 173 >; 8 amto2 Pm. 
Dublin, Luoyp ; ae 5 — = 152 ; 3-Hourly. 
Hobarton, Kay z faa : - : ra ==: MDF 3; Hourly. 
Toronto, aoa aa! eee ; TOBE eel arse sf ; ‘i 
Lmrnoy | 18438 547 
Trevandrum, Broun ; aes : ae ee 1) 59 % 
: 9: 
” » 3 ee 3 = ==>, 1:57 % 
< zs ; aE ; = == 159 8 observations daily. 
f rok povieeatbeier ea nT ae y19taR 
It is difficult to say, from the quantities found, that there has been any 
marked difference in the amount of the maximum diurnal range of the magnetic 
needle at any given station since the commencement of the magnetic series of 
observations, with the exception of that for 1797. All the differences shown for 
the other epochs of maximum may be explained by the different methods of 
determining the amount of the oscillations. 
It will be observed, that the ratio of the yearly mean range at the maximum 
to that at the minimum, is nearly constant for stations so widely apart and so 
differently situated on the earth’s surface as Dublin, Toronto, Trevandrum, 
* This ratio for Munich is that for the true maximum and minimum; the three following ratios 
are from the greatest and least ranges, corresponding to the middle of each year. ‘They are also not 
from the same hours. 
{ The greatest yearly mean was the last from the hourly observations, 1848°25=11'69, as the 
yearly mean range at Dublin increased from that epoch to 1849°0 by 033, and at Munich to 1848'8 
by 0°03 ; the mean of these two increases has been added to the last yearly mean at Hobarton. 
t The last yearly mean from the hourly observations at Toronto (1848°0) was 11°65; the correc- 
tion to the maximum was derived from the Dublin observations, which showed very nearly the same 
amount of increase from year to year. Thus, the differences of the yearly mean ranges for the two 
places, Dublin minus Toronto, were— 
1844:0 1845:0 1846°0 1847°0 1848-0 
+0°54 + 0°37 +0"54 + 0°46 +0'58. 
The mean excess, 0°50, has been subtracted from the maximum range at Dublin, 1849°0 =13”31, to 
obtain the approximate maximum for Toronto. 


