I have grouped together æsthetic creations and scientific discoveries because they are associated by that moment of psychic excitation and extreme sensibility which brings together the most remote facts, the fecundating moment which has rightly been called generative, a moment at which poets and men of science are nearer than is generally supposed. Was there not an audacious imagination in Spallanzani’s experiments, in Herschel’s first attempts, in the great discoveries of Leverrier and Schiaparelli, born of hypothesis, which calculation and observation transformed into axioms? Littrow, speaking of the discovery of Vesta, observes that it was not the result of chance nor of genius alone, but of genius favoured by chance. The star discovered by Piazzi had glimmered in Zach’s eyes, but he, with less genius than Piazzi, or in a moment of less perspicacity, attached no importance to it. The discovery of the solar spots only needed time, patience, and good fortune, remarked Secchi; but it needed genius to discover their true theory. How many learned natural philosophers, observes Arago, in going down a river must have observed the fluttering of the vane at the mast-head, without discovering, like Bradley, the law of aberration. And how many artists, one might add, must have seen hideous heads of porters, without conceiving Leonardo’s Judas, or oranges without creating the cavatina of Mozart’s _Don Giovanni_. There is, however, one last objection which seems more serious. Nearly all great intellectual creations, and all discoveries of modern physics, are the results of the slow and continuous meditations of men of science and their predecessors; so that they form a kind of compilation, the chronology of which is not easy to define, because the date at which we are arrested indicates the moment of birth rather than of conception. This objection, however, may be applied to nearly all human phenomena, even the most sudden. Thus, fecundation is a phenomenon which depends on the good nutrition of the organism, and on heredity; insanity, death itself, though apparently produced by sudden, even casual, circumstances, are yet related on one side to the weather and on the other to organic conditions; so that often, one may say, the precise date is fixed at birth. CHAPTER II. CLIMATIC INFLUENCES ON GENIUS. Influence of great centres--Race and hot climates--The distribution of great masters--Orographic influences--- Influence of healthy race--Parallelism of high stature and genius--Explanations.