198 
DR. C. CHREE: DISCUSSION OF KEW MAGNETIC DATA 
representing sunspot minimum. The mean values of W olfer’s sunspot frequency for 
the years included in these three tables were respectively 417, 75'0 and 7 "2. Finally 
Table YIII. gives for each of the eleven years the mean diurnal inequality for the 
whole year. Tables IX. to XII. for V correspond exactly with the four tables for H. 
The n.c. element has been eliminated from all these tables in the way already 
described. All the inequalities refer to G.M.T. Kew local time is only \\ minutes 
after Greenwich, so the employment of local time would have made little difference. 
§ 6. The other inequalities were calculated from the H, Y and D inequalities, taking 
the latter as given in my previous paper. We have 
T 2 = H 2 + Y 2 , tan I = Y/H, N = H cos D, W = H sin D . . . (l). 
Thus if AT, AH, &c., represent corresponding small departures from the mean 
values we have 
AT = cos I AH + sin I AY, 
AI = l sin 21 (AY/V- AH/H), 
AN = cos D AH —H sin D AD, 
AAV = sin D AH + H cos D AD 
The coefficients of AH, AY, &c., on the right-hand sides of these equations varied 
slightly throughout the eleven years, in consequence of the secular change. They 
were treated as constant throughout individual years, and mean values were taken 
for inequalities based on the eleven years. In the latter case the formulae actually 
used were 
AT = 0-384 AH + 0'923 AY, 1 
AI = 0’0277 5 AY —0'0668 AH, 
y .3 . 
AN = 0-955 AH—D58 AD, i 
AW = 0-298 AH+5-08 AD 
where the unit is 1' in the case of Al and AD, and ly in the case of the force 
elements. 
Table XIII. gives diurnal inequalities for T. The results for the 12 months are 
from the 11 years combined. But in addition to a diurnal inequality for the year 
from the 11 years combined, there are corresponding inequalities for the sunspot 
maximum and minimum groups of years. 
For I two inequality tables are given. Table XIY. contains inequalities for the 
12 months and the whole year from the 11 years combined, being derived from 
Tables A'. and IX. It also contains diurnal inequalities for the year from the sun¬ 
spot maximum and minimum groups of years. Table XA r . gives diurnal inequalities 
for the whole year, from the separate years, based on Tables VIII. and XII. 
Tables XAH. and XAHI. give monthly and seasonal diurnal inequalities for N and AY 
