102 THE POPULAR SCIENCE MONTHLY. 



uted to a fresh student of the applied sciences. As the discoveries of 

 Galileo, Kepler, Newton, Dalton, Cavendish, Gauss, displayed ever- 

 new phenomena following mathematical laws, the theoretical exact- 

 ness of the physical universe was taken for granted. Now, when peo- 

 ple are hopelessly ignorant of a thing, they quarrel about the source 

 of their knowledge. Accordingly, many maintained that we know 

 these exact laws by intuition. These said always one true thing, that 

 we did not know them from experience. Others said that they were 

 really given in the facts, and adopted ingenious ways of hiding the 

 gulf between the two. Others, again, deduced from transcendental 

 considerations sometimes the laws themselves, and sometimes what, 

 through imperfect information, they supposed to be the laws. But 

 more serious consequences arose when these conceptions derived from 

 physics were carried over into the field of Biology. Sharp lines of 

 division were made between kingdoms, and classes, and orders ; an 

 animal was described as a miracle to the vegetable world ; specific 

 differences, which are practically permanent within the range of his- 

 tory, were regarded as permanent through all time ; a sharp line was 

 drawn between organic and inorganic matter. Further investigation, 

 however, has shown that accuracy had been prematurely attributed to 

 the science, and has filled up all the gulfs and gaps that hasty observers 

 had invented. The animal and vegetable kingdoms have a debatable 

 ground between them, occupied by beings that have the characters of 

 both, and yet belong distinctly to neither. Classes and orders shade 

 into one another all along their common boundary. Specific differ- 

 ences turn out to be the work of time. The line dividing organic 

 matter from inorganic, if drawn to-day, must be moved to-morrow to 

 another place ; and the chemist will tell you that the distinction has 

 now no place in his science except in a technical sense for the con- 

 venience of studying carbon compounds by themselves. In geology 

 the same tendency gave birth. to the doctrine of distinct periods, 

 marked out by the character of the strata deposited in them all over 

 the sea ; a doctrine than which, perhaps, no ancient cosmogony has 

 been further from the truth, or done more harm to the progress of 

 science. Refuted many years ago by Mr. Herbert Spencer, 1 it has 

 now fairly yielded to an attack from all sides at once, and may be left 

 in peace. 



When, then, we say that the uniformity which we observe in the 

 course of events is exact and universal, we mean no more than this : 

 that we are able to state general rules which are far more exact than 

 direct experiment, and which apply to all cases that we are at present 

 likely to come across. It is important to notice, however, the effect 

 of such exactness as we observe upon the nature of inference. When 

 a telegram arrived stating that Dr. Livingstone had been found by Mr. 

 Stanley, what was the process by which you inferred the finding of 

 1 "Illogical Geology," in Essays, voL i. Originally published in 1859. 



