CLASSIFICATION 51 



considered in relation to the total extent of knowledge and 

 the opportunities which at the time existed of checking 

 speculation by observation. If it were possible to construct 

 a diagram showing the extent in every age of the means of 

 attaining knowledge, and the deviations from truth, and 

 approaches to truth of natural philosophers ; and then to 

 express the attainments of each epoch as fractions, with the 

 mean truthfulness as numerator, and the opportunities of 

 reaching truth as denominator, it is possible that the result 

 would not be creditable to the present generation. Anyone 

 reading the history of science should form such a mental 

 diagram in which the man with unaided senses, the Greeks, 

 Romans, Arabs, scholars of the seventeenth century, the 

 eighteenth century and the Victorian Age, take their places. 

 Their attainments should never be estimated except in re- 

 lation to their opportunities. 



Ample materials are to be found in the "Encyclopaedia 

 Britannica" for studying the history of science. We have 

 space only to ask what is the most impressive burthen of 

 such study. The great gain which the ages have brought to 

 science is the increasing purity of aim of its votaries. 

 Formerly knowledge was a means to a practical end. Now 

 it is an end in itself. To take a simple illustration from 

 the history of chemistry : The ancients were acquainted 

 with a certain number of substances, some of which when 

 placed in water passed into solution; some when ignited 

 disappeared in flame ; some when heated with charcoal were 

 resolved into an earthy calx and a bright metal. They had 

 no conception of the part played by the atmosphere in com- 

 bustion a substance when burnt disappeared in flame. 

 They had no clear notion of the nature of a compound 

 matter when combined with other matter was transmuted 

 into new matter, a change in its nature was marked by a 

 change in appearance and properties. What conclusion 

 more rational than that matter could be created and de- 

 stroyed, that it was protean, any substance being change- 



