OF NATURE. 579 



attempts towards a systematic exposition of the funda- 

 mental conceptions on which the exact sciences are built 

 up. Especially are we indebted to Prof. Mach for 

 applying his epistemological principles in three im- 

 portant regions of scientific inquiry : in the science of 

 dynamics, which he has to a large extent remodelled; 

 in the analysis of sensations ; and lastly, in the theory 

 of heat. Views similar to his have been elaborated in 

 this country, as it appears independently, and in an 

 original manner, by W. K. Clifford, and, more sys- 28. 



J Clifford and 



tematically, by Prof. Karl Pearson in his ' Grammar K - Pearson, 

 of Science' (1st edition, 1892). In fact, they do not 

 widely differ from opinions already expressed by Herbert 

 Spencer in several of his earlier works, notably in his 

 'Principles of Psychology' (1st edition, 1855), and his 

 'First Principles' (1862); they had been popularly 

 explained in his replies to criticisms that appeared 

 in the 'Quarterly Eeview ' (1874) and the 'British 

 Quarterly Keview ' (1873). These replies are reprinted 

 in the third volume of his ' Collected Essays.' 



The rationale and result of all these discussions can be 

 summed up in the thesis : that the whole system of 

 conceptions by which the exact sciences try to describe 

 the observable and known phenomena of nature, and to 

 predict those that are unknown and frequently escape 

 observation, is symbolic, a kind of shorthand, uncon- 

 sciously invented and perfected for the sake of con- 

 venience and for practical use ; that the leading 

 principle is that of Economy of Thought. 



Through this latter conception Prof. Mach's Thought 7 - f 

 opinions come into contact with those of Eichard 



