238 Setentific Intelligence. 
was impossible to see through a thickness of 5 cm. of it. }t 38 
calculated that more than 200 tons of sulphur are burned with the 
coal every winter’s day in London, and this quantity is sufficient, 
in the writer’s opinion, to account for London ogs.— Nature, 
iT 
: M 
netic Deelination and Horizontal force, as observed from 1841 to 
at the Roy w 
Solar Spot frequency ; by Witt1aM ELL Is, F.R.A.S.—Observa 
tions of the magnetic elements have been carried on at Green- 
wich since 1841. Until 1847 actual readings of the various instru: 
ments were taken at two-hour intervals, but since the beginning 
of 1848, in addition to the absolute determinations of declina- 
tion, intensity and dip, a continuous record of the variations of 
the declination and the horizontal and vertical components of 
registration, devi by Mr. Charles Brooke. e fact that 
during long period the observations of the declination and 
h 1 force, discussed in this n the 
ial value to 
em 
mean diurnal range of declination in each month 18 taken 
the month; and similarly “for the horizontal force. his mean 
diurnal range for each month is obtained by taking the differ- 
ence between the greatest and least of the mean indications for 
each separate hour through the month, days of great magne ef 
disturbance being rejected. A table is thus formed givin 
series of numbers: the variation in declination is expresse®’ 
minutes of arc; for the variation of the horizontal force the unit 
is 0001 of thé whole horizontal force. The numbers thus ob- 
tained show a marked increase for the summer months. | d 
annual inequality having been, by special calculation, eliminate, 
a second table is formed giving the annual mean of the monthly 
