CHAP. XII.] CORRESPONDENCE. 399 



KirchofFs notions in beginning of Vorlesungen (not 

 equal to Lagrange, but worth noticing). 



I also think that Clausius' equation and definition of 

 " Virial " is important. 



The dynamics of other varieties of space than our own 

 requires very brief notice indeed. Yours truly, 



J. CLERK MAXWELL. 



TO W. GrARNETT, Esq. 



Glenlair, Dalbeattie, 24th July 1877. 



. . . There is a great slur over the word mechanics since 

 a few poets and biologists have misused it. Pratt thought 

 it a fine word. 



The result of motion without reference to time I call 

 Displacement. Kinematics must involve the idea of time if 

 it treats of continuous displacements, velocities, and accelera- 

 tions, though it does not contain within itself materials for 

 comparing different intervals of time. For this we must go 

 to the science which deals with matter ; call it Kinetics, 

 Dynamics, or Mechanics. 



But I consider that Statics also deserves a place on the 

 same level as Kinematics, as it deals with the equivalence 

 of different systems of forces. But I do not agree 

 with Whewell that Statics is more elementary than Kine- 

 matics. . . . 



To THE SAME. 



Glenlair, lltfi August 1877. 



Your experiments on electrified paraffin oil are excellent, 

 and may lead to increase of knowledge. 



If the fluid dielectric and also the air are perfect 

 insulators, nothing can get electrified, but the equation at the 

 surface, instead of being P = P , will be 



dV 



(excluding capillary action) where is the resultant 



dv 



