54 Proceedings of the Royal Physical Socvety. 
The seasonal distribution of sunshine at Strathpeffer, in so 
far as it may be judged by the observations of a single year, 
is given in Table X., in comparison with Westminster. 
Spring is marked by a high percentage of sunshine, that is 
TABLE Xi 
Percentage of Possible 
Hours of Sunshine. | Duration. 
1890. 
Strath- West- Strath- West- 
peffer. Minster. peffer. minster. 
Winter (Dec., Jan., Feb.), 139 65 19°2 8:0 
Spring (March to May), . 440 343 34°0 26°3 
Summer (June to August), 383 382 a5" 26°7 
Autumn (Sept. to Nov.),. 261 252 27°8 24°8 
by an exceptionally clear atmosphere, whilst in summer the 
percentage was considerably less, and indeed fell slightly 
below the Westminster standard. It is particularly notice- 
able that the winter months show a total of 139 hours against 
65 in London. 
The winter sunshine of these islands, and particularly of a 
station to which invalids are accustomed to resort, is a matter 
of especial interest, and the question suggests itself whether 
it is possible to form an approximate statement of the actual 
value of the winter radiation, say at Strathpeffer Spa and at 
London. In the first place the records show that in spite of 
a mean loss of an hour in length of the winter day, the 
duration of measurable radiation is in proportion of more 
than two to one in favour of the northern station. Secondly, 
this duration, as recorded, represents nearly one fifth of 
possible duration at Strathpeffer, and a little more than one- 
twelfth at London (192 per cent. and 8:0 per cent. respec- 
tively). Now it appears from the calculation of zenith 
equivalents that for the average winter day in London the 
mean zenith value of radiation is 2°66 hours, and at Strath- 
peffer 1°32 hour approximately. The fraction one-twelfth, 
expressing duration, obviously cannot be taken as an expres- 
sion of intensity or value. For what affects the instrument - 
on a winter’s day is, as a rule, the comparatively intense 
