78 HEAT, ELECTRIC AND MOLECULAR VIBRATION. 



CHAPTER XI. 



POPULAR DOCTRINES OF ELECTRIC AND MOLECULAR 

 VIBRATION, DENOTED HEAT. 



HE RE are so many theories of heat and light 

 as sources of motive -power, that our limits 

 will permit us to notice but a few of the most 

 recent. 



A summary of existing scientific opinions, orig- 

 inating from distinguished philosophers and chem- 

 ists, appears to be embodied in a treatise on " Heat 

 Considered as a Mode of Motion," by John Tyn- 

 dall. 1 Other more definite treatises have been 

 written at various times, from which this popular 

 writer has gleaned various views. 



He begins the investigation with the following 

 words : 



"What is the agent by means of which we can over- 

 power the force of the winds and rivers ? The achieve- 

 ments of heat by the steam-engine have impressed upon 

 thinking minds this important question." 



He continues : 



"Let us commence our researches with heart and 

 hope. If we succeed, we shall satisfy, to an extent 



1 D. Appleton & Co., New York, 1867. 



