485 
ON “QUIET” DAYS DUEING THE ELEVEN YEAES 1890 TO 1900, ETC. 
those deduced froiii Table I. Ouiittui^' the three mouths already referred to, we have 
125 monthly changes common to the two sets of frequencies. Of these 97 agree, 
and 28 differ in sign. If, however, we take only those cases in which tlie monthly 
change amounted to at least 10 in one or other of the two sets of data, we find an 
agreement in sign in no less than 60 cases out of 72. 
Passing to the monthly changes in the percentage ^-alues of the I) and H ranges, 
given 111 fables XXXIII. and XXXI\., we find there also frequent alternations of rises 
and falls. For instance, in Table XXXllL, rises and falls alternate without a break 
fiom January, 1893, to January, 1894. On the whole, however, there are appreciably 
fewer transitions of sign in the I) and H Tables than in Table I. When the montlilv 
changes in the two sets of sun-spot frequencies differ in sign, the changes in 
lahles XXXIII. and XXXIV. agree sometimes with the one set, sometimes with the 
other, there being in hotli tables a very slight preponderance of agreements with 
Wolfe us all day frequencies. This may lie purely accidental, lint at all events the 
magnetic changes agree at least as well with the sun-spot data from all days as with 
those from quiet days only. 
§ 74. There still remains the ipiestion whether there is a distinct connection 
lietween the mean values for individual months of sun-spot frequencies and magnetic 
ranges. In the case of H there does seem fairly definite evidence of such a connec¬ 
tion. If we take the changes of sign we have jnst been considering in Tables I. 
and XXXIV., we find an aoTeement in sign in 74 cases, as against disagreement in 
55 cases , and if Ave confine ourselves to cases where the changes between successive 
mouths values, in Table I., is at least 10, we find agreement in 34 cases out of 50. 
This amount of agreement is more than would he at all likely to happen l)y pure 
chance. In the case of I), however, the agreements and disagreements in sign are 
almost equally numerous, and even vdien we confine ourselves to cases where the 
sun-si)ot change was at least 10 tlie balance of agreements is too small to he relied on. 
In the case of H a diurnal range of 50y is exceptionally large; the curve is read 
only to ly ; the average non-cyclic effect is 3y, and there may he a small uncertainty 
through temperature. Thus the uncertainty in individual figures in Table XXXlAk 
cannot well he less than 2 oi- 3 per cent, even at midsummer. In the case of D, the 
lange often exceeds 10', a]id seldom falls heloAv 5'; the curve is read to O'vl ; the 
non-cyclic effect is very small, and there is no temperature correction. Thus the 
unceitainty in individual figures in Table XXXlll. should l)e considerably less than 
m Lahle XXXI\ . I bus the absence of an unmistakable connection between I) ranges 
and sun-spot frequencies in individual Jiionths has stronger evidence in its favour than 
has the apparent connection between H ranges and monthly sun-spot frecpiencies. 
If instead of individual months we take years the connection is clear, and it is 
manifest enough, eveii m D, for considerably shorter periods than years at times when 
sun-spot frequency has a rapid general drift in one direction. 
§ 75. Some light on the degree of intimacy of the connection is derivable from the 
3 K 2 
