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The tendency indicates that there is a large body of 

 readers who are so far instructed in the elements of 

 science as to be able to understand these summaries. 

 In England, Germany, France and this country such 

 brief essays are abundant, either in the form of con- 

 tributions to popular and scientific journals, or in 

 that of popular lectures, or in that of brief manuals, 

 or of monographs on separate topics ; especially 

 such topics as are novel, or are interesting to the 

 public for their theoretic brilliancy, or their applica- 

 tions to industry and art. 



These essays need not be and they are not always 

 superficial, because they are brief. They often are 

 the more profound on account of their conciseness, 

 as when they contain a condensed summary of the 

 main principles of the art or science in question, 

 or a brief history of the successive experiments 

 which have issued in some brilliant discovery. 

 These essays are very generally read, even though 

 they are both concise and profound. But they could 

 not be read even though they were less profound 

 than they are, were there not provided a numerous 

 company of readers who are sufficiently instructed 

 in science to appreciate them. That such a body 

 of readers exists in the countries referred to, is 

 easily explained by the existence of public schools 

 and schools of science and technology, by the 

 enormous extension of the knowledge of machinery, 

 engineering, mining, dyeing, etc., etc., all of which 

 imply a more or less distinct recognition of scien- 

 tific principles and stimulate the curiosity in regard 

 to scientific truth. Popular lectures also, illustrated 

 by experiments, have been repeated before thousands 



