POPULAR WEATHER PROGNOSTICS.
By the Hon. Ralph Abercromby, F. M. S., and William Marriott, F. M. S., reprinted from the “Quarterly Journal of the Meteorological Society,” published in London.
The attempt to foretell the weather is not of recent date; the ancients carefully studied the sky and clouds, and endeavored to predict the kind of weather that was likely to ensue; and a number of the popular prognostics of the weather of his time are recorded by Aristotle in his work on meteors. In later times our forefathers studied the weather, and as they had no instruments to guide them they observed natural objects and noticed the appearances of the sky and clouds, and also the movements of animals, birds, plants, &c. Shepherds and sailors especially being exposed to all kinds of weather, would naturally be on the lookout for any signs of a coming change, and after a time would begin to associate certain appearances with certain kinds of weather. A good deal of weather wisdom of the above character has been thrown into proverbs, trite sayings, and popular verse; and we propose in the present paper to examine and explain some of these by the aid of the most recent discoveries of meteorological science. A great advance has been made in meteorology during the last twenty years, owing to the introduction of daily synoptic charts of the distribution of atmospheric pressure, temperature, wind, rain, &c. From these it is evident that there is a distinct relation existing between the distribution of pressure and the direction and force of the wind, and the temperature and weather generally. A glance at a number of the charts shows that there is nearly always present either an area of low pressure, called a cyclone, usually having an approximately circular form, and, as a rule, moving in an easterly or northeasterly direction; or an area of high pressure, called an anticyclone, also nearly circular in form, but almost stationary in position. The wind in all cases also blows in a direction nearly parallel with the isobars, having the region of lowest pressure on the left hand. This has given rise to the simple law propounded by Dr. Buy’s Ballot, for the northern hemisphere, viz: “Stand with your back to the wind, and the barometer will be lower on your left hand than on your right.” In cyclones the wind circulates in the opposite way to which the hands of a watch move, but exhibits usually a little in-draught; while in anticyclones the wind circulates in the same way as the hands of a watch, but exhibits usually a little outward motion. The intensity of the wind in all cases depends upon the closeness of the isobars; for the closer the isobars the greater is the difference in pressure in a given distance, and consequently the stronger the wind. Nearly all of our weather is of the cyclonic or anticyclonic type, and is entirely dependent upon the form and distribution of the isobars. It is, therefore, by the aid of isobaric charts that we shall attempt to explain popular prognostics, and to associate them with certain kinds of weather. The method of research actually adopted has been for many years past to take notes of any good observation of any prognostic and put them in a portfolio, with the nearest synoptic chart available, or preferably with the nearest, both before and after. When a sufficient number had been collected they were analyzed, and the remarkable result has been arrived at that the greater number of prognostics are simply descriptive of the weather and appearance of the sky, in the different portions of the various shapes of isobars seen on synoptic charts, and that they indicate foul or fair weather just as they precede the shifting areas of rain or blue sky which are mapped out by the isobaric lines. These charts not only show the success of the prognostics, but also explain wherein they sometimes fail, by tracing the changes of each particular condition of the weather. Hitherto the only prognostics which have been accounted for have been those due to excessive damp, but by means of isobaric charts many others can be readily explained. It must not be supposed that the modern methods diminish the value of prognostics, for even in forecasting weather from synoptic charts they are of great value, and are always exceedingly useful to solitary observers who have only a single barometer to depend upon besides these prognostics, as, for instance, on board ship.
We hope that the present paper will create an interest on the part of many in this subject, and show that it is within their power to assist in advancing the science of meteorology, so that it may not remain any longer in the unsatisfactory state set forth in the following old Bedfordshire lines:
“Well, Duncombe, how will be the weather?”
“Sir, it looks cloudy altogether,
And coming across our Houghton Green,
I stopped and talked with old Frank Beane.
While we stood there, sir, old Jan Swain
Went by and said he knowed ’twould rain;