MODELS AND APPARATUS 



FOB ILLUSTRATING 



THE PHENOMENA OF HEAT, THE STEAM ENGINE, Ac, 



FIG. 2995. FIG. 2946. 



FIG. 2996. 



FIG. 3003. 



FIG. 2997. 



HEAT. 



" IN the study of nature two elements come into play, which belong respectively to 

 the world of sense and to the world of thought. "We observe a fact, and seek to 

 refer it to its laws ; we apprehend the law, and seek to make it good in fact. The 

 one is Theory, and the other is Experiment, which when applied to the ordinary 

 purposes of life becomes Practical Science. Nothing could illustrate more forcibly 

 the wholesome inter-action of these two elements than the history of our present 

 subject, viz., Heat. If the Steam Engine had not been invented, we should assuredly 

 stand below the theoretic level which we now occupy. The achievements of heat 

 through the steam engine have forced, with augmented emphasis, the question upon 

 thinking minds : ' What is this agent, by means of which we can supersede the force 

 of winds and rivers, of horses and men ? ' 



" Heat can produce mechanical force, and mechanical force can produce heat ; 

 some common quality must therefore unite this agent and the ordinary forms of 

 mechanical power. The relationship established, the generalising intellect could 

 pass at once to the other energies of the universe, and it now perceives the principle 

 which unites them all. Thus the triumphs of practical skill have promoted the 

 development of philosophy. Thus by the inter-action of thought and fact, of truth 

 conceived and truth executed, we have made our science wha,t it is the noblest 

 growth of modern times, though as yet but partially appealed to as a source of 

 individual and national might." Heat a Mode of Motion, by JOHN TYNDALL, 

 LL.D., F.R.S., Prof, of Nat, Philosophy in the Royal Institution of Great Britain. 



2 I 



