ON MATTER AND FORCE. 29 



Mr. Clifford, in his lecture at the Koyal 

 Institution, says : " Fourier, in trying to find 

 the laws of the spread of heat from one part of 

 a body to another, took the hypothesis that 

 heat was a fluid which flowed from the hot end 

 into the cold as water flows through a pipe. 

 From this hypothesis the laws of conduction 

 were deduced; but, in the process, it was 

 found that the very same laws would flow 

 from other hypotheses. In fact, whatever can 

 be explained by the notion of a fluid, can be 

 equally well explained either by the attraction 

 of particles or by the strains of a solid sub- 

 stance. The very same mathematical calcula- 

 tions result from three distinct hypotheses." 



With regard to the third stage of ideas 

 regarding the union of matter and electric and 

 magnetic force, Dr. Whewell says, the discovery 

 of the polarisation of heat shook the idea of the 

 electric fluids as physical realities. Material 

 caloric and material electricity fell together. 



Mr. Grove says : " Electricity is that affec- 

 tion of matter or mode of force which most 

 distinctly and beautifully brings into relation 

 other modes of force, and exhibits to a great 

 extent, in a qualitative form, its own relation 



