330 THE POPULAR SCIENCE MONTHLY, 



'Tis negation's hour of triumph, 

 In the absence of the sun ; 



'Tis the hour of endings, finished, 

 Of beginnings unbegun. 



Yet the voice of awful silence 

 Bids my waiting spirit hark ; 



There is action in the stillness, 

 There is progress in the dark. 



In the drift of things and forces, 

 Comes the better from the worse, 



Swings the whole of Nature upward, 

 "Wakes, and thinks a universe. 



There will be more life to-morrow, 

 And of life, more life that faiows; 



Though the sum of force be constant, 

 Yet the Living ever grows. 



So we sing of Evolution, 



And step strongly on our ways, 



And we live through nights in patience, 

 And we learn the worth of days. 



In the silence of murk midnight 

 Is revealed to me this thing : 



Nothing hinders, all enables 

 Nature's vast awakening. 



-- 



HISTORY OF THE DYNAMICAL THEORY OF HEAT. 1 



By POETEE POINIEE. 



II. 



ABOUT one year after the reading of the famous paper of Rum- 

 ford, in the early part of 1799, Sir Humphry Davy, then but 

 twenty years of age, published his first scientific memoir, entitled 

 " An Essay on Heat, Light, and the Combinations of Light." Clear- 

 ly enunciating the two systems of hypothesis previously held, he 

 chose to follow Newton in rejecting the materiality of heat, while 

 still clinging to the corpuscular or emission theory of light. 



His position with respect to the existence of caloric he asserted in 

 this thesis : 



" The Phenomena of Repulsion are not dependent on a pe- 

 culiar Elastic Fluid for their Existence, or Caloric does not 



1 Introduction to an unpublished work on Thermo-Dynamics. 



EXIST 



