December 22 – Future past

Today’s factismal: Benjamin Franklin’s “Meteorological  Imaginations and Conjectures” was published for the first time 229 years ago.

I’ve mentioned Benjamin Franklin before, and the important role that he played in both science and diplomacy; it is not a stretch to say that without Franklin, there might not have been an America. And today is a special day for fans of Franklin because it marks the 229th anniversary of the first publication of one of his more important (though lesser known) papers. Called Meteorological  Imaginations and Conjectures, this paper discussed several basic phenomena and introduced a new idea that is still in use today. Because it is so hard to find, I’ve taken the liberty of reproducing the text below:

Meteorological  Imaginations and Conjectures. By Benjamin Franklin , LL.D F. R. S. and acad. reg. Scient. Paris. Soc. etc. Communicated by Dr. Percival. Read December 22, I784.

 

There seems to be a region higher in the air over all countries, where it is always winter, where frost exists continually, since, in the midst of summer on the surface of the earth, ice falls often from above in the form of hail. Haistones, of the great weight we sometimes find them, did not probably acquire their magnitude before they began to descend. The air, being eight hundred times rarer than water, is unable to support it but in the shape of vapour a state in which its particles are separated. As soon as they are condensed by the cold of the upper region, so as to form a drop, that drop begins to fall. If it freezes into a grain of ice, that ice descends. In descending, both the drop of water, and the grain of ice, are augmented by particles of the vapour they pass through in falling, and which they condense by their coldness, and attach to themselves. It is possible that, in summer, much of what is rain, when it arrives at the surface of the earth might have been snow, when it began its descent; but being thawed, in passing through the warm air near the surface, it is changed from snow to rain. How immensely cold must be the original particle of hail, which forms the center of the future hailstone, since it is capable of communicating sufficient cold, if I may so speak, to freeze all the mass of vapour condensed round it, and form a lump of perhaps fix or eight ounces in weight!

 

When, in summer time, the sun is high, and continues long every day above the horizon, his rays strike the earth more directly, and with longer continuance, than in the winter; hence, the surface is more heated, and to a greater depth, by the heat of those rays. When rain falls on the heated earth, and falls down into it, it carries down with it a great part of the heat, which by that means descends still deeper.

 

The mass of earth, to the depth perhaps of thirty feet, being thus heated to a certain degree, continues to retain its heat for some time. Thus the first snows that fall in the beginning of winter, seldom lie long on the surface, but are soon melted, and soon absorbed. After which, the winds that blow over the country on which the snows had fallen, are not rendered so cold as they would have been by those snows, if they had remained. And thus the approach of the severity of winter is retarded; and the extreme degree of its cold is not always at the time we might expect it, viz. when the sun is at its greatest distance, and the day shortest, but some time after that period, according to the English proverb which says, “as the day lengthens, the cold strengthens” the causes of refrigeration continuing to operate, while the sun returns too slowly and his force continues too weak to counteract them.

 

During several of the summer months of the year 1783, when the effect of the sun’s rays to heat the earth in these northern regions should have been greater, there existed a constant fog over all Europe, and great part of North America. This fog was of a permanent nature; it was dry, and the rays of the fun seemed to have little effect towards dissipating it, as they easily do a moist fog, arising from water. They were indeed rendered so faint in passing through it, that when collected in the focus of a burning glass they would scarce kindle brown paper. Of course, their summer effect in heating the earth was exceedingly diminished. Hence the surface was early frozen; hence the first snows remained on it unmelted, and received continual additions. Hence the air was more chilled, and the winds more severely cold. Hence perhaps the winter of 1783-4, was more severe, than any that had happened for many years.

 

The cause of this universal fog is not yet ascertained. Whether it was adventitious to this earth, and merely a smoke, proceeding from the consumption by fire of some of those great burning balls or globes which we happen to meet with in our rapid course round the sun, and which are sometimes seen to kindle and be destroyed in passing our atmosphere, and whose smoke might be attracted and retained by our earth; or whether it was the vast quantity of smoke, long continuing; to issue during the summer from Ilecla in Iceland, and that other volcano which arose out of the sea near that island, which smoke might be spread by various winds, over the northern part of the world, is yet uncertain . It seems however worth the enquiry, whether other hard winters, recorded in history, were preceded by similar permanent and widely extended summer fogs. Because, if found to be so, men might from such fogs conjecture the probability of succeeding hard winter, and of the damage to be expected by the breaking up of frozen rivers in the spring; and take such measures as are possible and practicable, to secure themselves and effects from the mischiefs that attended the last.

 

Passy, May 1784.

Though the paper includes a lot of interesting ideas (how hailstones form, transport of heat by storms, temperature lag), but perhaps the most interesting is the last one – that changing the atmosphere’s composition can change the amount of light that it lets through and so can create an unusually strong winter (or summer). He was proven right just 32 years later when Mount Tambora erupted and created “the year without a summer”.

Today, we are still interested in ideas about climate. And the way that scientists judge ideas like Franklin’s is by how closely the predictions match the observations. But that means that the scientists need someone to make the observations –  and that’s where you come in! The Citizen Weather Observer Program needs people (lots and lots of people) who are willing to host a weather station in their backyard and give it bandwidth to transmit weather observations every five minutes. The scientists then use that data to do what Franklin suggested: discover what will happen next so that we can prevent disasters. If you’d like to take part, flash on over to:
http://wxqa.com/index.html

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