Mat 11, 1917] 



SCIENCE 



449 



carried the smaller conception to general 

 acceptance. 



So fundamental a theory as that of 

 Laplace to explain the origin of the uni- 

 verse, a theory which has been standard 

 doctrine for more than a century and is 

 only now being replaced as a result of 

 rigidly applied tests, appears never to have 

 been very seriously considered by its 

 author, but was thrown off as a brief ap- 

 pendix or postscript to a general work on 

 astronomy. It has the curious title "Note 

 VII. and Last ' ' and Laplace says of it that 

 the hypothesis must be received "with the 

 distrust with which everything should be 

 regarded that is not the result of observa- 

 tion or calculation." Moreover, so far as 

 known, Laplace never subjected the theory 

 to the test of well-known mathematical 

 principles which were involved, although 

 this was his usual habit. The success and 

 general acceptance of the theory seem tO' 

 have been due to the altogether remarkable 

 prestige of its author as the greatest 

 mathematician since Newton, and as the 

 author of the ' ' Mecanique Celeste, ' ' a work 

 which has never been rivaled in its field, 

 and of which it has been said that any one 

 of its twenty-four parts would have made 

 the reputation of a man of science. 



Though primarily a theory of the origin 

 of the universe and thus in the realm of 

 astronomy, Laplace's nebular hypothesis 

 left its impress upon geology and partic- 

 ularly upon geophysics, in that it gave con- 

 tinued standing and scientific respectabil- 

 ity to the notion that the earth has a liquid 

 interior. It would be somewhat difficult 

 to trace the origin of this belief, which 

 naturally grew up from the observations 

 of volcanic eruptions — no uncommon event 

 in the Grecian Archipelago and in Italy, 

 the regions where science had its begin- 

 nings. After the studies of combustion had 

 exploded the notion of "internal fires," 



the theory took the form which it has re- 

 tained to our day, little affected at first by 

 the proofs of earth rigidity which were 

 brought forward by Kelvin. With little 

 doubt the associated idea of a congealed 

 crust floating upon a liquid interior is 

 based upon the analogy with the winter 

 cover of ice which forms over our lakes 

 and rivers. This analogy supplies, there- 

 fore, a striking instance of the influence of 

 climate in giving complexion to a funda- 

 mental theory, and the fact that rock, un- 

 like water, is heavier in the solid than in the 

 liquid state, is a very recent discovery. 

 Save for its intimate relation to Laplace's 

 theory, the conception of the liquid core to 

 the earth must have long since been rele- 

 gated to the limbo of exploded doctrines^ 

 to the great benefit of more than one of the 

 physical sciences. 



It would be easy to show that well-known 

 scientific theories have embodied fatal de- 

 fects, in that assumptions of vital impor- 

 tance have been introduced quite uncon- 

 sciously by their authors. I have believed, 

 and have elsewhere attempted to show, that 

 the Pratt-Hayford theory of isostatic com- 

 pensation, which assumes for every moun- 

 tain a necessary defect of mass directly be- 

 low, and for the column below every de- 

 pression of the earth's surface a corre- 

 sponding excess of mass; that this theory 

 has been set up without due regard to the 

 dominating effect of any hidden masses of 

 unusually high density which may lie near 

 the observing station. This view seems 

 now to have found confirmation in recent 

 studies carried out by the United States 

 Coast and Geodetic Survey. I may perhaps 

 best illustrate what is here meant by the use 

 of an example taken from a related field of 

 study. If one should ascribe the strong 

 magnetic attraction which is exercised by 

 local masses of iron ore in the Northern 

 Peninsula of Michigan to the effect of such 



