316 A SHORT HISTORY OF SCIENCE 



Fire, long a mystery, was by this time regarded, not as an "ele- 

 ment," but as a luminous centre of intense chemical change. 

 Water, above all, abundant, important, susceptible of metamor- 

 phism into ice, snow, dew, fog, and steam, had surrendered the 

 secrets of its very being, having been split apart into hydrogen and 

 oxygen gases, and created or restored as a liquid by bringing these 

 two gases together at high temperature. Here also, as in Frank- 

 lin's kite experiment, mystery, if not dispelled, was at least driven 

 back ; and the suggestion became natural and reasonable, If 

 only enough were known, might not many other mysteries in na- 

 ture be lessened, if not altogether done away ? 



But, while these more comprehensible and more rational ideas 

 of air, fire, and water were now the common property of natural 

 philosophy, natural history still held unsolved most of its ancient 

 problems. The earth, for example, while probably no longer re- 

 garded as one of the four elements, was as yet a standing puzzle 

 in respect to its origin, both as a whole and as to its parts. 

 Astronomy had proved the planetary character of the earth 

 but had not yet suggested for it or for its fellows any natural, 

 as opposed to supernatural, origin, and was entirely silent as to 

 the sources and history of the earth's crust, so rich in minerals, 

 metals, volcanoes, earthquakes, soils, craters, gases and par- 

 ticularly fossils, those mute remains which could no longer 

 be disposed of as freaks of nature, but must be looked upon 

 as indefeasible witnesses to a prehistoric past. Leonardo in 

 the fifteenth and Palissy in the sixteenth century revived the 

 ideas of Pythagoras and Xenophanes as to the true nature of fos- 

 sils, but no further progress of note was made for upwards of a 

 hundred years, when about 1670 Steno, a Dane, and Scilla, an 

 Italian, published studies on petrifactions, illustrated with draw- 

 ings. Hooke, already referred to (p. 268), Ray, the naturalist, and 

 later (1695) Woodward, made collections of chalk, gravel, coal, 

 and marble, and gravely discussed their meaning in terms of the 

 Flood of Noah. In this unsatisfactory position matters stood at 

 the end of the seventeenth century, and it was not until nearly the 

 middle of the eighteenth, viz. in 1740, that much further progress 



