304 
POPULAR SCIENCE REYIEW. 
has submitted to the Royal Astronomical Society some extracts from 
meteorological notes taken in Gibraltar from 1860 to 1867, and further in- 
formation respecting the weather since the last date. The extracts, &c., 
refer to the last fortnight in December, and the following summary cannot 
but be regarded as affording the Spanish eclipse-expedition very good 
promise. 
There were from December 15 to December 31 in the year 
1860 
6 very good days, 
6 fair days, 
and 5 indifferent 
1861 
3 
V 
5 
ii 
9 
ii 
1862 
10 
11 
6 
ii 
1 
n 
1863 
13 
11 
3 
ii 
1 
n 
1864 
5 
11 
10 
ii 
2 
a 
1865 
12 
11 
H 
ii 
* 
ii 
1866 
6 
11 
9 
ii 
2 
n 
1867 
8 
11 
5 
ii 
3 
a 
1868 
11 
11 
5 
ii 
1 
ii 
1869 
7 
11 
9 
ii 
1 
n 
Floor of Plato. — Mr. Birt continues to collect observations having refer- 
ence to the degree of visibility of spots upon the Floor of Plato. The num- 
ber of spots seen on the Floor of Plato up to the present time is 35, eight of 
which have been detected since Sept. 27, 1869. Since then no less than 
■531 observations have been made. The degree of visibility of each spot is 
indicated in a long and elaborate table, the indications of which are thus 
summed up by Mr. Birt : — u The number of spots, in which an increase of 
visibility has taken place, is nearly equal to that in which a decrease ha3 
occurred, viz., ten of the former and eleven of the latter. Spot No. 3, a 
craterlet, has manifested the greatest increase, while spot No. 19 has 
exhibited the largest decrease. The extent of variation of the separate 
spots is very irregular, and does not appear to indicate the operation of any 
general law. In one or two instances only have neighbouring spots been 
similarly affected.” He concludes thus : — “ The observations of the twelve 
lunations ending in March 1870, extend considerably the basis on which to 
found an intelligible explanation of the phenomena ; it is nevertheless much 
too narrow to hazard more than conjecture. Another year’s observations 
will doubtless throw further light on the subject.” 
Association between Sun-spots and Magnetic Declination Changes. — Prof. 
Wolf has instituted a comparison between recent changes in the condition 
of the sun’s surface and the diurnal variations of the magnetic declination 
ns observed at Christiania. It is worthy of notice that Professor Wolf had 
adopted an empirical formula for indicating the association between sun- 
spot periods and periods of declination or variation ; so that the inquiry now 
instituted tends to determine how far what was in effect a prediction has 
been confirmed by the result. The calculated formula (from observations 
made in the years 1852-61) was for Christiania — 
v = 0'0413r + 4'*921 * 
where v is the mean declination variation for the year, r the relative number ' 
indicating the frequency of sun-spots during the year. The following table 
indicates the calculated and the observed variations v and v ' during the years 
1864-69. 
