There are, however, terrestrial causes to which the irregularities of our curve (which irregularities, be it remembered, represent regularly recurring irregularities of heat) may be ascribed. For instance, there can be no doubt that our climate is considerably affected by the changes which take place in the Polar seas; and it may not unfairly be assumed that the processes by which different regions of Polar ice are successively set adrift (to be carried southward by the strong undercurrent known to exist in the northern Atlantic Ocean), take place at epochs which recur with tolerable regularity. And it may be that the irregularity of the rising as compared with the falling of the heat-curve is due to this cause; since the breakmg-up of ice-fields and their rapid transport southwards would clearly produce sudden changes, having no counterpart in the effects due to the gradual process of freezing.1
It may well be, however, that the observations of forty-three years are not sufficient to afford the true mean diurnal temperature for a climate so variable as ours. Indeed, if the curves given by Kaemtz for continental climates be as accurately indicative of observed changes as that of Fig. 3, we must either accept such an hypothesis, or else assume that the English climate is marked by regularly recurring variations altogether wanting in continental climates; and it is to be noted that the regular recurrence of changes is a peculiarity wholly distinct from variability of climate, properly so termed, and seems even inconsistent with such a characteristic. It may happen, therefore, that the observations of the next thirty or forty years will afford a curve of different figure; and that by comparing the observations of the eighty or ninety years, which would then be available, many, or all, of the irregularities exhibited in Fig. 3 might be removed. In this case we might expect our climate-curve to assume the form indicated by the light line taken through the irregularities of Fig. 3. It will be observed that this modified curve exhibits but one maximum and one minimum. It is not wholly free, however, from variations of flexure. It presents, indeed, six well-marked convexities, and as many concavities; in other words, no less than twelve points of inflexion. The most remarkable irregularity of this sort is that exhibited near the end of November; and it is noteworthy that this irregularity is presented by continental climate-curves also. It has been ascribed by Ertel to the effect of the meteor-zone which causes the November shower. But as it is exhibited by the curves of horary as well as of diurnal means, while the meteor-zone cannot by any possibility affect the temperature of the earth's following hemisphere, and as, further, it does not correspond to the true date of the shower, this view may be looked upon as doubtful. The August curve occurring near the maximum elevation-where slow change was to be expected, is also well worthy of notice; as are the January and May flexures.
1 Icebergs have been seen travelling southwards against a strong northward surface-current, and even forcing their way through field-ice in so travelling.
It will be noticed that nothing has been said of extreme heat or cold occasionally experienced in England. As such visits generally last but for a short time, their effects are not very injurious, save on the very weak, the aged, or the invalid. Corresponding to the passage of an immense heat-wave or cold-wave, there invariably occurs a sudden rise in the mortality-returns; but almost as invariably the rise is followed by a nearly equivalent, but less sudden fall; showing conclusively that many of the deaths which marked the epoch of severest weather occurred a few weeks only before their natural time.
The weather during a part of the late winter was somewhat severer than our average English winter-weather. The thermometer, however, at no time descended below zero, as it did on January 3, 1854; and the diurnal mean did not descend at any time so low as 10° 7', as it did on January 20, 1838. There is no foundation for the opinion, sometimes expressed, that our winter weather is changing. An examination of the columns in the Greenwich meteorological tables, show that the successive recurrence of several mild winters is not peculiar to the last decade or two. The observations of Gilbert White, imperfect as they are compared with modern observations, point the same way.
Among severe, but short, intervals of cold weather may be noted that which occurred in January 1768. The frost was so intense, says Gilbert White, 'that horses fell sick with an epidemic distemper which injured the winds of many and killed some; meat was so hard frozen that it could not be spitted, nor secured but in cellars; and bays, laurustines, and laurels were killed.'
White's account of the summer of 1783 will fitly close our sketch of British weather-changes. 'This summer,' he says, 'was an amazing and portentous one, and full of horrible phenomena; for besides the alarming meteors and tremendous thunder-storms that affrighted and distressed the different counties of this kingdom, the peculiar haze or smoky fog that prevailed for many weeks in this island, and in every part of Europe, and even beyond its limits, was a most extraordinary appearance, unlike anything known within the memory of man. By my journal, I find that I had noticed this strange occurrence from June 23 to July 20, inclusive, during which period the wind varied to every quarter, without making any alteration in the air. The sun at noon looked as blank, and ferruginous as a clouded moon, and shed a rust-coloured ferruginous light on the ground and floors of rooms, but was particularly lurid and blood-coloured at rising and setting. All the time the heat was so intense that butchers' meat could hardly be eaten the day after it was killed; and the flies swarmed so in the lanes and hedges, that they rendered the horses half frantic, and riding irksome. The country people began to look with a superstitious awe at the red, louring aspect of the sun. Milton's noble simile, in his first book of "Paradise Lost," frequently occurred to my mind; and it is, indeed, particularly applicable, because, towards the end, it alludes to a superstitious kind of dread, with which the minds of men are always impressed by such strange and unusual phenomena: -
As when the sun new risen, Looks through the horizontal misty air, Shorn of his beams; or, from behind the moon, In dim eclipse, disastrous twilight sheds On half the nations, and with fear of change Perplexes monarchs.'
Intellectual Observert March 1867.