224 GALE OF JAN., 1845, AT GREENWICH AND ORKNEY.

preceded by lightning and thunder. The minimum reading occurred first at the southern places, and afterwards at the northern :-thus, at Greenwich at 12h. 53m.; at Cambridge, 1h. 35m.; and Manchester, at 2h.-GLAISHER.

Having thus minutely detailed the circumstances of the storm of the 13th of January, 1843-in which the barometer displayed its faithfulness, although suspected of an error-let me briefly advert to one instance more of its action at Greenwich and Orkney.

I have briefly, indeed far too briefly, adverted to some points of the year 1845-a year of magnitude exceeding most in the importance of its events.

1845

March 27th, at 9 A.M., Greenwich Barometer 29.67

S.W. breeze at Greenwich, pressure of from four to five pounds.

March 28th, at 9 A.M., Greenwich Barometer 29.53

W.S.W. gale, pressure of eight pounds, and frequent

GREENWICH AND ORKNEY RESPONDING AREAS. 225

gusts, with nine to ten pounds on the square inch of Osler's anemometer.

1845

March 28th, at 9 P.M., Greenwich Barometer 29.64

Orkney

29.32

Difference

W.S.W. breeze, pressure of only one to two pounds, and at midnight nearly calm.

Greenwich

⚫32

The balance turned, and a N.W. light air, with pressure of half a pound.

I conceive it to be almost impossible to adduce more positive demonstration of the strict alliance between the wind and the barometer. As the pressure between the two places varied, so directly and immediately did the wind, and I believe the action to be instantaneous; and provided we had a series of the same delicate observations at other places like those we have at Greenwich, I doubt not, in the least, that the action was quick almost as the electric telegraph. As it is, we have the broad and general fact, and such an approximation as to render the opinion probable. It may be desirable just to advert to the point that the barometer at Orkney, on 28th March, 1845, was 28-60, with a strong S.W. gale there; but January 13th, 1843, the barometer was 28 56; they had no gale at all. So far

226 VALUE OF DELINEATION FOR INSPECTION.

the appearances and indications of the barometer were the same, and yet the results were so widely differing— in the one case a gale, and the other none. The comparison with the Greenwich barometer explains the whole. In March, 1845, the Greenwich barometer was nearly one inch above the Orkney; hence a strong rush of air from Greenwich, or the southward; but in January, 1843, the barometers soon approximated, and the Orkney barometer was highest, hence no southerly breeze or air from Greenwich.

Returning now again to our delineation. It will be found to supply us with ample materials for safe and sound deductions and explanations of many circumstances that occur. I have often been very much surprised, when a S.W. or W.S.W. gale has blown fresh and strong throughout the day, to find it lull and die away frequently at night-fall; and I could not perceive any reason for it, until I had made some collateral delineations of my own observations on the barometer with those which I subsequently received from Orkney; and then, as in the delineations I have prefixed, it will be perceived that the Orkney barometer has a frequent tendency to rise so much more through the day than the Greenwich one, and to approximate each other at 9 P.M. Thus, upon the evening of the 4th to the morning of the 5th, a rise at Orkney and a fall at Greenwich. Again, on the 8th and 10th of January, but particularly so on the 28th and 30th. In these cases the wind was checked more or less at Greenwich, and lulled by the antagonistic rise at

THE DELINEATION DISPLAYS ALL THE POINTS. 227

Orkney, and the wind more or less altered in its

course.

In many cases the veering of the S.W. to W., is caused by the opposing northern pressure at Orkney, which deflects our S.W. to W., and puts it about sometimes completely.

The barometer, when the N.W. wind is coming, rises first at Orkney, and they appear to have more frequent N.W. winds there than at Greenwich.

I could dilate much more upon my humble delineation. The days of highest and lowest barometer do not uniformly accord at Greenwich and Orkney-they may do so, or be reverse states. There are two new moons given in January, 1843. They do not appear to produce the same state of the barometer nor the weather at either place; and so on, throughout each delineation the same differences are exhibited. But every one must judge for themselves.

I have been very particular in stating as my opinion that we owe our mild winters to the prevalency of S.W. winds arising from a continuous higher pressure in the Madeira area; but that alone would not be sufficient, unless not only we had a lower, but that Orkney had a still lower barometer than Greenwich. The delineation exhibits this part of the fact beautifully, the black or Orkney is almost uniformly below the red or Greenwich. Hence room was made for the S.W.

winds to blow into. The Orkney low, and the Madeira high barometer, procure our favouring gales and mild

winters.

228

S.W. WINDS FLOW INTO THE POLAR REGIONS.

It will be perceived, therefore, we had a vast pre

winds and scarcely any N.W.,

ponderance of S.W. and those only short. The N.E. were absent, and the mean temperature of January, 1843, was 40°, or 4° above the mean, being a soft, warm, mild month, and the early spring flowers appeared.

The Rev. C. Clouston, in his letter to me, says, that at Orkney, January, 1843, has been very wet and boisterous, and changeable. On the 4th, frequent showers, squalls, and hail showers, and hail so large as to break twenty-three windows on the west side of his house in one minute. And again on the 7th, thunder and lightning, and hail, which broke thirteen windows more the pieces of hail were one inch in length-ovate or egg-shaped, and were accompanied with much lightning and thunder, which is more common with us than in the " summer."

One question more presents itself ere we close the subject of these S.W. winds. Observing how frequent they are, and from whence they come, and whither they go, we may ask what becomes of their heavy freight of vapour? It is no wonder that Scotland abounds with lakes, and that the northern regions have such copious streams and abundant supplies of water, seeing that these winds come loaded with vapour, and are ever impelled on one side or other towards the polar region, which is the separate condenser of the vast volumes of steam raised in the warm regions, and impelled towards these climates.