;i9G ])K. C. CIIllEE: ANALYSIS OF EESULTS FROM THE mV MAGNETOGEAPHS 
§ 38. Considering first the last column of Table XXX., we see that the agreement 
})etween the observed and calculated monthly values is on the whole best for D and 
H, and worst for V. This is in accordance Avith what we would expect from instru¬ 
mental considerations. Even for Y the agreement is very good. Except in the case 
of the mean percentage error does not exceed 9, while in the case of the ranges 
and the sum of the 24 hourly differences from the mean, it does not exceed 7. In 
the case of the quantities concerned are so small that an error of 15 per cent, 
represents but a small fraction of O'T or ly, the least quantities actually measured. 
This shows that annual and semi-annual terms suflace to give a very accurate repre¬ 
sentation of the annual variation, and that little would be gained by introducing 
higher terms in the Fourier series."^ 
Coming next to the ratios, we see that in the case of the ranges, the 24 hourly 
differences, and C]^, the phenomena presented are fairly similar in all the elements ; Ave 
luwe Pi/M Aurrying only from 0'42 to 0’67, and Po/M A'arying only from 0'07 to 0T5. 
In the case of Co the Amine of P.^/M is nearly the same for all the elements ; but, 
compared to the annual term, the semi-annual term is relatiA’ely much more important 
in I and IT than in D and Y". 
The relatrte importance of the semi-annual term is much greater in C 3 than in or 
f.,; and in the semi-annual term is much the more important of the tAvo, especially 
in the case of I and H. 
It Avill be noticed that, speaking generally, the Anrlues of P^'/M difler less in the 
seAmral elements than do the A'alues of P]/M, and that there is a close resemblance 
between the phenomena in I) and Y^, and again IjetAA’een the phenomena in I and H. 
Coming next to the phase angles, Ave see that excluding the different quantities 
considered sIioav pretty similar residts, and that the angles in the annual and seml^ 
annual terms do not differ much. It is probably most instructiA'e to consider not so 
much the angles themselves, as the results deduced from them for the times of 
occurrence of the maxima in the seAmral terms. In the case of the annual terms 
there is only one maximum. Taking, for example, the declination range, aa’b find the 
angle corresponding to the maximum of the annual term from the equation 
t + 275° = 450°, or t = 175°. 
This anSAvers to 177 days from the beginning of the year, going only to the nearest 
Avliole day, and may be taken as ansAvering to June 26. The minimum occurs six 
months later. 
A semi-annual term has of course tAvo maxima separated liy six months, with two 
minima, at three months inteiwals from the maxima. In the case of the declination 
range> for instance, the first maximum Avould ausAver to 
2t + 273° = 450°, or t = 88°-5. 
This may be taken as representing 89 days from the beginning of the year. 
* See ‘Brit. Assoc. Report’ for 1890 , p. 223. 
