To Hunt a Star - Four Revolutions in the Earth Sciences - page 150

led Gilbert to “suspect that it is the scar produced by the collision of the earth with
a small star. The indications are that the missile is somewhere under the scar.” 11
Like Thomas Chamberlin, Gilbert was an exponent of the proper methodology
of science and of the principle of multiple working hypotheses. Five years before
heheardFoote'slecture,inanarticletitled“TheInculcationoftheScientificMeth-
od by Example,” Gilbert wrote that
the great investigator is primarily and preeminently the man who is rich in hypotheses. The
man who can produce but one cherishes and champions that one as his own, and is blind to its
faults. With such men, the testing of alternative hypotheses is accomplished only through con-
troversy. Crucial observations are warped by prejudice, and the triumph of truth is delayed. 12
Gilbert's own thinking about lunar craters, together with the report of a col-
league whom he sent to Arizona to study Coon Mountain, as the feature had come
to be called, led him to conclude that it could have formed in one of two ways:
volcanic steam might have blasted forth from underground, producing a cavity
but leaving no telltale evidence of volcanism, or a meteorite might have crashed
and excavated the crater. In his logical way, Gilbert devised tests to discriminate
between the two. If an underground explosion had ejected the material that once
occupiedthecrater,thatsamematerial,withitssamevolume,shouldnowbefound
scattered around the rim. On the other hand, as Gilbert later described his reason-
ing, if a “star entered the hole the hole was partly filled thereby and the remain-
ing hollow must be less in volume than the rim.” 13 Thus comparing the volume
of ejecta with the volume of the crater would provide a first test. The second test
would come from the telltale magnetism that a “buried star” would leave behind.
No magnetism, no meteorite.
In 1891, Gilbert took a leave of absence and set out for Flagstaff, the town
nearest to the crater and the future home of the USGS's Astrogeology Branch.
Once on site, Gilbert, the quintessential field geologist, enjoyed the experience.
“We were free to stop where we pleased, and we always stopped where there was
plenty of fuel,” he wrote. “So we didn't mind if we had to comb ice from our hair
after morning ablutions.” 14
AsGilbert later described his attitude at the start ofthe fieldwork, “the presump-
tion was in favor of the theory ascribing the crater to a falling star, because the
theory explained, as its rival did not, the close association of the crater with the
shower of celestial iron.” He estimated the “probability of non-coincidence to be
at least 800 times as great as the probability of coincidence,” odds that, though
they did not prove “a causal relationship . . . legitimately [incline] the mind toward
causality.” 15