608 LAMONT: MAGNETIC RESULTS 
There are no movements in the diurnal march which are not 
sufficiently determined by hourly observations; those taken in- 
termediately show us rapidly passing irregularities, but contri- 
bute nothing to the determination of the regular movements. 
The following table shows how far the terms can be success- 
fully applied to the determination of the mean declination, and 
of its annual variation. In this table the mean of the two-hourly 
observations of the thirty preceding and thirty following days is 
taken as the ¢rwe declination. 
Declination deduced from Correction of the results. 
Term. |True Declina- | 
tion. The whole| Every The even | The whole| Every | The even 
term. hour. hours. term. hour. hours. 
1040; | ee f ’ ; é ‘ ; 
Aug. ...| 16 60°36 | 59°54 59-50 57°90 | +.0°82 | + 0°86 | + 2-46 
Sept. 59°24 59°57 59:97 60:55 | — 0-33 | — 0°73 | — 131 
Octinesce- 58°77 59-18 59-07 59-72 | — 0-41 | — 0:30 | — 0°95 
Nov 58°07 | 57:97 | 57°71 | 57-69 | + 0-10 | +036 | + 0-28 
Dec... 57-47 | 55°61 | 55°72 | 55°60 | + 1-86 | + 1-75 | + 1-87 
1841. 
Hebavcusey 56-93 | 57:08 56°90 56:06 | —015 | + 0:03 | + 0°87 
April ...| 5564 | 5460 | 54:87 | 54:94 | + 1-04 | +077 | + 0:70 
May ...... 55°56 | 53:87 | 53:69 | 53:50 | + 1-69 | +187 | + 2-06 
JPNE aes 53°37 54°74 54-71 54:63 | — 1:37 | — 1:34 | — 126 
RUS: sales 53°25 53°73 53°84 54:01 | —0-48 | — 059 | — 0:76 
Aug. ... 52-47 52°85 52°74 53:11 | —0-38 | — 0-27 | — 0°64 
Sept 51-72 | 51:70 51°65 51:84 | + 0-02 | + 0:07 | — 0:12 
ets ...003 50°90 49-00 49°11 48:72 | + 1:90 | +1:89 | + 2°18 
Nov 51:07 51-20 51-23 50°65 | — 0-13 | —0-16 | — 0°42 
Dec 50°60 50°65 | 50-40 50:94 | — 0-05 | + 0:20 | — 0°34 
The probable errors of the means for the whole term, for every 
hour, and for the even hours, are to each other as 
POs Oe) 14. 
We see that it is quite indifferent for the determination of the 
mean declination whether observations are taken every hour or 
every five minutes. The somewhat greater amount of the pro- 
bable error of the mean of the even hours can only be regarded 
as accidental; for if we were to omit a few days on which the 
greatest deviations took place, the difference would nearly dis- 
appear. 
What has been said of the declination is also true of the in- 
tensity, except that the deviation of the several days from the 
mean is much greater in the intensity than in the declination. 
to the southern hemisphere : it appears also to have been a day of very great 
disturbance both in the Declination and Horizontal Intensity at Prague. The 
term-day of August 1840 was also a day of considerable disturbance, showing 
itself in both hemispheres.—E. S. ] 
