ON COMPARISON AND REDUCTION OF MAGNETIC OBSERVATIONS, 241 
whole earth at precisely the same moment of absolute time (see ‘ Proc. 
Roy. Soc.’ vol. liii p. 191). But an instantaneous magnetic shock 
sensible over the whole globe could scarcely, one would imagine, arise 
from action from within alone ; and since magnetic disturbances are more 
frequent when sunspots are numerically high, there seems reason to 
‘suppose that the exciting cause is in such cases mainly external. To 
pursue this matter is, however, rather to enter the region of speculation. 
It may perhaps be remarked that the mean non-cyclic change for 
horizontal force and vertical force on ‘quiet’ days is +40 and — 18 
respectively ; also that the mean excess of absolute value on such days over 
all days is correspondingly + 34 and — 8 respectively. Thus the rela- 
tion in both elements is of the same character. 
A part of my work consisted of a comparison of diurnal inequalities 
of the magnetic elements on ‘quiet’ days with those found by including all 
days (always excepting the excessive magnetic disturbances), and also of 
4 comparison of diurnal range as given: (1) by ‘quiet’ days as observed ; 
{2) by ‘quiet’ days corrected for non-cyclic change ; and (3) by including 
all days, in all cases for the different months of the year ; but the work 
is not sufficiently advanced to enable any particulars to be given. 
Dr. Chree, referring to a previous report of the Magnetic Committee 
and to a paper by Messrs. Robson and Smith in the ‘Phil. Mag.’ for 
August 1890, speaks of the differences between diurnal ranges deduced 
from unrestricted days, that is all days, and from ‘quiet’ days. I may 
perhaps point out that these comparisons were between ‘ quiet’ days at Kew 
and all days at Greenwich, and were for the element of declination only. 
In such a comparison the question of difference of locality must be taken 
into account, and also possibly to some extent the difference of instruments. 
But in a paper which I communicated to the ‘ Phil. Mag.’ for January 1891 
I made a more direct comparison of results, for the one year 1889, compar- 
ing the diurnal inequalities for ‘quiet’ days (five in each month) at 
Greenwich with those for all days at the same place. This comparison 
4was made for all the three elements of declination, horizontal force, and 
vertical force. The five-day results were not corrected for non-cyclic 
change, but in declination and vertical force this was evidently small. 
The results show a marked difference between the diurnal inequalities for 
4quiet’ daysand for all days. The later work in this direction, yet incom- 
plete, to which I have above referred, includes a discussion of the diurnal 
inequalities for the five years 1890 to 1894 for ‘quiet’ days and for all 
days, and the results seem likely to support those found for the single 
year 1889. 
Solar Radiation.— Twelfth Report of the Committee, consisting of Sir 
G. G. Sroxes (Chairman), Professor H. McLEop (Secretary), 
Professor A. ScuustER, Mr. G. JOHNSTONE STONEY, Sir H. E. 
Roscor, Captain W. pe W. Asney, Mr. C. Curer, Mr. G. J. 
Symons, and Mr. W. E. Witson, appointed to consider the best 
Methods of Recording the Direct Intensity of Solar It«adiation. 
«Drawn up by Sir G. G. STOKEs.) 
Av the date of the tenth report of this Committee, Professor McLeod, 
who had undertaken to make some experiments with the Stewart’s 
actinometer used as a ‘dynamical’ actinometer, tried whether it might 
1896. R 
