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The Great Earthquake
When The Great Earthquake struck New England, learned men blamed everything from God’s wrath to an overabundance of lightning rods in Boston. Two hundred and twenty-five years later, geologists are at last discovering the true causes.
August/September 1980 | Volume 31, Issue 5
In 1749 Georges Leclerc, Comte de Buffon, of Paris had suggested an age of seventy-five thousand years for the earth, which he speculated had been created from solar matter after the collision of a comet and the sun. The long-standing assertion that the earth’s surface had been created from the condensation of minerals suspended in the Mosaic flood would soon face an opposing view that subterranean fire shaped the earth’s crust. Known as the Neptunists and the Vulcanists (or Plutonists), both schools were partly right.
Fire, and occasionally water, dominated the speculation about earthquake causes that arose in the colonies after the 1755 shocks, which produced the first attempts to probe such an event with scientific inquiry. Dr. Thomas Prince, who was pastor of Old South Church, acknowledged hypotheses by “the projecting Sort of Philosophers both ancient and modern” over “a central Concave of fire [or] a vast internal Abyss of Waters.” Then he projected his own theory, adding the phenomenon of electricity, lately described by Benjamin Franklin, to his list of earthquake causes.
God, Dr. Prince explained, had created an earth “of very loose Contexture,” in which existed numerous caverns filled with “Sulphurious, nitrous, fiery, mineral and other Substances such as those in the Clouds, which are the natural Causes of Thunder and Lightning.” The underground collision of these substances meant an explosion and, hence, an earthquake.
But earthquakes formed merely “a Twentieth Part of our imminent danger,” Prince announced. Citing Robert Boyle’s law of the pressure of gases, he warned that the “terrible atmosphere” blanketing the earth presses the ground with a weight of 2,592 pounds per square foot. After a subterranean explosion, he said, vapors escape, leaving a vacuum. The menacingly heavy air around us, “this astonishing Weight, besides that of the Earth, immediately bares away everything before it into the Space below.” Entire hills and cities had thus been pressed underground by the air.
Prince further refined his theory of electrical causes of earthquakes by suggesting that Boston had suffered worse shocks because of its abundance of lightning rods, then called iron points. The rods had been installed after 1751 at Benjamin Franklin’s suggestion, in a city that had last been ravaged by fire as recently as 1747. Prince suggested that they conveyed extra electricity into the earth from the sky and thus imperiled Boston.
Enter an incredulous Harvard professor. “Philosophy, like everything else, has had its fashions,” John Winthrop IV scoffed in response to Prince, “and the reigning mode of late has been to explain everything by ELECTRICITY.... Now, it seems, it is to be the cause of earthquakes.” The earth, he noted, was barred by simple laws of physics from creating electricity. And as for Prince’s lightning-rod theory, Winthrop answered, “I cannot believe that in the whole town of BOSTON, where so many iron points are erected, there is so much as one person, who is so weak, so ignorant, so foolish, or, to say all in one word, so atheistical, as ever to have entertained a single thought, that it is possible, by the help of a few yards of wire, to ‘get out of the mighty hand of GOD.’ ”
Winthrop, Hollisian professor of mathematics and natural philosophy at Harvard, continued his public tiff with Prince, whom he often referred to as “the Rev. Divine,” for several months. Colonists looked to the two of them for answers to the Cape Ann earthquake—which both men incorrectly believed to have come from the northwest. Winthrop, who had introduced Newton’s fluxions, or calculus, to the United States and opened the nation’s first experimental physics laboratory, was probably the most scholarly of colonists to contribute to the earthquake literature, if not the most prescient.
Flame and pent vapors, he believed, promoted earthquakes, a likelihood he supported by observing the abundance of tremors near volcanoes. Like Prince, he believed the quaking earth exhaled pent vapors, but, citing Newton, Winthrop suggested that the vapors might supply the atmosphere with “true, permanent air,” a mysterious but revitalizing substance.
Winthrop’s contribution to the imminent science of geology stems more from his careful, empirical descriptions and calculations of the Cape Ann earthquake events. By measuring effects, he carefully deduced the chronology and characteristics of the shock, applying physical maxims whenever he could. He documented the existence of both horizontal and vertical motion during a tremor, comparing the generation of earthquake “waves” to that of the vibrations of a struck musical chord, where an instrument’s strings bend broadly at first and then vibrate increasingly rapidly in returning to their stationary positions.