64 THE POPULAR SCIENCE MONTHLY. 



that the memory of children is better than the memory of adults. In 

 truth, average children remember far less in quantity than adults, and 

 they remember different things according to their age and taste. With 

 children as with adults, and as with prodigies, the memory, scientifically 

 studied, is an exact measure of mind, and in all, old and young, its 

 limitations are so great as to impair most seriously the value of most 

 of human testimony, even in matters of every-day life ; while in all 

 science, or the capacity of the human brain for observing systematized 

 knowledge, for thinking and for remembering, is so limited that the 

 world must defend, and practically, in the face of all the teachings of 

 logicians and authorities on evidence, does defend, and rests its faith 

 exclusively on, the testimony of experts, and in claims of new discov- 

 eries, especially against antecedent probability, on the testimony of a 

 few only, and those of the very highest character experts of experts 

 the opposing testimony of millions and millions of non-experts, though 

 concurring and including the best and wisest of mankind, through all 

 the ages being justly regarded as worse than worthless. 



-+++- 



THE GEOWTH OF THE STEAM-ENGINE. 1 



By Peofessob E. H. THUKSTON, 



OF THE STEVENS INSTITUTE OF TECHNOLOGY. 



VI. 

 THE STEAM-ENGINE OF THE FUTURE, AND ITS BUILDER. 



HAVING thus rapidly outlined the history of the steam-engine, 

 and of some of its most important applications, we may now take 

 up the question 



What is the problem, stated precisely and in its most general form, 

 that engineers have been attempting here to solve ? 



After stating the problem, we will examine the record with a view 

 to determine what direction the path of improvement has taken hither- 

 to ; and, so far as we may judge the future by the past, by inference, 

 to ascertain what appears likely to be its course in the present and in 

 the immediate future. Still further, we will inquire what are the con- 

 ditions, physical and intellectual, which best aid our progress in perfect- 

 ing the steam-engine. 



This important problem may be stated in its most general form 

 thus: 



To construct a machine which shall, in the most perfect manner 

 fiossible, convert the kinetic energy of heat-motion, as derived from 



1 An abstract of " A History of the Growth of the Steam-Engine," to be published 

 by D. Appleton & Co. 



