23 
instance in the month of May of a complete absence of 
ozone during 24 hours, and this instance occurred in 1859. 
Taking the means of the monthly values given in the 
table for each year, we have the following annual values : 
Annual 
Means 
at lOh. p.m. 
Annual 
Means 
at lOh. a.m. 
General 
Annual 
Means. 
1856.... 
..... 4*92 ... 
... 3*50 .... 
.. 4*21 
1857 
3-19 ... 
... 2*46 .... 
.. ' 2-82 
1858.... 
..... 2-58 ... 
... 3-61 .... 
.. 3 ’09 
1859 
..... 2-06 ... 
... 2*91 .... 
.. 2*48 
1860 
1-78 ... 
... 2*65 .... 
.. 2-21 
1861.... 
2-44 ... 
... 3-71 .... 
... 3-07 
1862.... 
3-77 ... 
... 4-98 .... 
... 4-37 
1863 
4-62 ... 
... 5-50 .... 
.. 5-06 
1864.... 
4-22 ... 
... 4-23 .... 
.. 4*22 
1865.... 
4-25 ... 
... 4-36 .... 
... 4-30 
According to Mr. Mackereth’s results the annual amounts 
of ozone are greatest when the intensity of solar radiation is 
greatest, or when solar spots are most numerous; but a 
glance at the last of the above columns of numbers shows 
that at Oxford this relation does not hold good : on the con- 
trary, the annual amounts of ozone are least when solar 
spots are most frequent or the intensity of solar radiation 
greatest ; and this is especially the case with the amounts 
of ozone observed during the day. Thus the mean annual 
amount of ozone for both day and night during the years 
1858-62, when the number of solar spots was above the 
average for the ten years, was 3 ’04, and for the remain- 
ing five years 4T2 ; whilst the mean annual values of the 
day amounts alone for these periods were respectively 2*52 
and 4’24. The corresponding mean annual values of the 
night amounts were 357 and 401. 
Gomparing the mean day and night amounts for the years 
