The butterfly effect has become a popular metaphor for sensitive dependence on initial conditions—the hallmark of chaotic behavior. I describe how, where, and when this term was conceived in the 1970s. Surprisingly, the butterfly metaphor was predated by more than 70 years by the grasshopper effect.

1.
Edward N. Lorenz, The Essence of Chaos (University of Washington Press, Seattle, 1994).
2.
Edward N.
Lorenz
, “
The predictability of hydrodynamic flow
,”
Trans. N. Y Acad. Sci.
25
,
409
432
(
1963
).
3.
The Chaos Avant-Garde, Memories of the Early Days of Chaos Theory, edited by Ralph Abraham and Yoshisuke Ueda (World Scientific, Singapore, 2000). See pp. 91–92.
4.
James Gleick, Chaos (Viking, New York, 1987). Gleick writes: THE LORENZ ATTRACTOR (on facing page). This magical image, resembling an owl’s mask or butterfly’s wings, became an emblem for the early explorers of chaos. This is historically incorrect because the image was not produced as such until the late 1970’s.
5.
Robert C. Hilborn, Chaos and Nonlinear Dynamics (Oxford University Press, Oxford, 2000), 2nd ed.
6.
Edward N. Lorenz, letter to Oliver M. Ashford, 27 December, 1989.
7.
Ray Bradbury, “A sound of thunder,” in R is for Rocket (Bantam, New York, 1962).
8.
Edward N. Lorenz, letter, 1 May, 1990, to Robert C. Hilborn.
9.
Philip Merilees, letter, 28 August, 1990, to Robert C. Hilborn.
10.
George R. Stewart, Storm (Random House, New York, 1941). In a telephone conversation, Lorenz told me that after reading an early draft of this paper, he recalled the Chinaman metaphor from having read the Stewart novel and that this novel was influential in his decision to go into meteorology.
11.
H. G. Schuster, Deterministic Chaos (VCH, New York, 1984).
12.
W. S.
Franklin
, Review of P. Duhem, Traité Élémentaire de Méchanique fondée sur la Thermodynamique (Paris, 1897), Vols. 1 and 2, in
Phys. Rev.
6
,
170
175
(
1898
).
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