THE CLIMATE OF GUERNSEY TYPICAL.

133

with the other islands-must be regarded as typical in respect of climate.

To be satisfied that this is the case, the reader need only refer to the physical map at the end of this volume, and consider the relative positions of all the islands and the nearest land. Alderney is within seven miles of France, and has an important group of rocks protecting it from the west. Jersey is double the size of Guernsey, only half the distance of the latter island from France, and is more in the heart of the great bay. Sark is very peculiar in its extreme smallness and the near approach made by its surface to a level, lofty table land; but as respects climate, it must receive the westerly winds after they have left Guernsey, and the easterly winds before they reach it; thus, in every sense, rendering Guernsey the typical island.

Under these circumstances, it cannot but be regarded as eminently fortunate, that since only one of the Channel Islands has had the advantage of systematic observations, extending over several years, this island should be Guernsey; and in referring to the annexed tabular view, it is satisfactory to be able to direct attention to it as containing a near approach to absolute results. The period of observation does not include the years since 1858, inasmuch as they have been exceptional in many respects, and probably form part of a cycle not yet completed, whilst the sixteen years selected appear to complete two climatal cycles.

N.B. The instruments employed in making the observations from which the table is constructed were as follows:—(1.) Barometer; made by Henry Barrow ; compared with the standard by Mr. Glaisher. (2.) Thermometers; dry and wet bulb and maximum instruments made by Negretti and Zambra, index error determined by Mr. Glaisher; minimum thermometer made by Newman, on Rutherford's construction; all four feet from the ground, and many yards from other objects. Wet and dry thermometers read at 9 a.m. and 3 p.m. Minimum and maximum, at 9 a.m. Corrections for daily range applied from Mr. Glaisher's tables; barometer correction for elevation above sea level not applied. (3.) Rain Gauge; a copper funnel and cistern; the contents measured by a graduated glass jar. Instrument twelve feet from the ground, and quite free from the influence of trees and buildings.

FROM JANUARY 1st, 1843, TO DECEMBER 31st, 1858.

BY S. ELLIOTT HOSKINS, M.D., F.R S., F.R.C.P., MEMBER OF THE BRITISH METEOROLOGICAL SOCIETY.
[Latitude of Station, 49° 27' N. Longitude, 2° 32′ W. Height of Station above mean sea-level, 204 feet.]

MEAN ANNUAL TEMPERATURE OF GUERNSEY.

135

The elements of climate may be considered to include the distribution of heat through the different days, months, and seasons, the variations of the pressure of the air as indicated by the barometer, the direction and force of the prevailing winds, the quantity of rain-fall and its distribution through the year, the dryness or moisture of the air from time to time, and the electric state of the air. To understand these fully, it will be necessary to refer to each in some little detail.

And first with regard to temperature. It will be seen from Dr. Hoskins's table, that the average annual temperature of Guernsey is 5130, and the following diagram will show how little this varies from year to year, and will also point to a significant fact, namely, that there has been during the period of observation one cycle of five years, during which the temperature was higher than the mean, succeeded by another cycle, also of five years, during which it was lower. We appear now to be entering a third cycle, which promises to be exceptional. The cycles of temperature do not thus appear to correspond exactly with the cycles of general climate.

53°

514

50

1843 '44 '45 '46 '47 '48 '49 '50 '51 '52 '53

DIAGRAM.

Illustrating the range of the mean annual temperature at Guernsey.

from 1843 to 1858 inclusive.

In the diagram, the middle line, 5140, marks the absolute mean, and the waved line, ranging above and below it, the actual mean of each year of the sixteen. The positions of the means of 50 and 53° (the extremes) are each indicated by a broken line.

The adopted mean temperature at Greenwich being 49°, it is evident, that on the whole, the climate of Guernsey may be regarded as 24° warmer. This, though itself a considerable increment, gives little idea of the nature or extent of the whole difference that exists between the two stations. In order to

The

obtain this, we must compare the different months and seasons, and then compare the daily ranges of the thermometer. former comparison will show any essential variety in the seasons, the latter any variety in the day and night temperatures. It would be quite possible for two stations to have the same mean annual temperature, the summer in one being very hot, and the winter very severe, while in the other the summer and early autumn are cool and uniform, and the winter and spring extremely mild. So also there would be a great difference in climate, if the average daily temperature of two places were the same, but in one, hot days were followed by frosty nights, while in the other the days were comparatively cool, and the nights never chilly.

As we must not here enter into much detail, it will be sufficient to make the comparisons in a general way. Taking the means determined by Mr. Glaisher, from observations extending from 1814 to 1856, as our standards of comparison for Greenwich, we have the following view of the relative climates of the two stations at different seasons of the year :

Whilst, therefore, the temperature of the year in Guernsey is only 20 above that of Greenwich, it appears that the autumn temperature is four degrees, and the winter as much as six degrees, warmer. On the other hand, there is only a difference of one degree in the spring months, and the summer months. are more than half a degree cooler in the island than in the south-east of England.

If, again, we take the six coldest months in the year, from November to April inclusive, and compare the temperatures of

COMPARISON WITH GREENWICH.

137

Guernsey and Greenwich, dividing this period into two parts,

The difference thus indicated is very marked, and points to the most favourable peculiarity of the Guernsey climate, namely, the continuance of a mild autumn temperature to a very late period of the year. It will be seen that the temperature of November at Greenwich corresponds with that of January in Guernsey, while November at Guernsey differs little from October at Greenwich.

If we take next the remaining three cold months, we shall recognise another of the Guernsey peculiarities; namely, the cold spring advancing but slowly into a cool summer. have the following elements of comparison :

Thus we

Hence, during spring months, the difference between the island and England gradually becomes less and less; the temperature in Guernsey advancing very much more slowly than at Greenwich. This continues through the succeeding months of summer, and it will be seen by the following figures; but between May and August, the differences are all in favour of England.