43 
observations, 1848-1857. 
follow : — 
January 9*5 
February 11*3 
March 131 
April 14-0 
May 12*7 
June 12’6 
The numbers in this table are as 
July 12-7 
August 12-6 
September 13*5 
October 122 
November 9 ‘3 
December 8*2 
The line No. 2, 
D 
in diagram D, is a projection of these 
numbers, and the line No. 1 is a repe- 
tition of curve 3, diagram C. It will 
be seen that the maxima and minima 
of the one correspond exactly with 
those of the other, and we are there- 
fore entitled to conclude that the two 
phenomena are intimately connected, 
and that the causes which produce 
variations in the intensity of solar radiation also affect th e 
diurnal oscillations of the magnetic needle. 
It was supposed by Sir William Herschel that the emission 
of heat from the sun varied according to the greater or less 
frequency of solar spots, and he attempted to support this 
view by a comparison of the prices of grain in years when 
the solar spots were numerous, with those in years when few 
or no spots were seen; but this kind of evidence was 
generally regarded as unsatisfactory, and it is, I believe, now 
generally admitted by meteorologists that the many valu- 
able series of thermometrical observations which have since 
been made in various localities, have hitherto failed to afford 
any decided indications of a periodical change in the element 
of mean annual temperature. The question therefore 
naturally arises, if the intensity of solar radiation varies in 
a period corresponding with the period of solar spot fre- 
quency, why does not the element of mean annual tempera- 
