DISCOVERT IN UNDEVELOPED PARTS OF SCIENCE. 467 



of others. One part of knowledge cannot make progress 

 until certain others have acquired a particular state of deve- 

 lopment. Some, therefore, must take the lead ; and when 

 the latter have advanced until they can proceed no farther, 

 the others must advance in their turn. Combinations of 

 circumstances occasionally occur which cause one science 

 to be more attractive and studied for the time being than 

 any other ; at one time it is astronomy, at another light, 

 heat, electricity, magnetism, chemistry, or biology. Simi- 

 larly, with particular branches of science and with par- 

 ticular arts, at one period electro-magnetism, at another 

 electro-metallurgy, and at another spectrum analysis has 

 been the engrossing subject. If a great discovery happens 

 to be made, or a startling effect produced, in one particu- 

 lar branch of science, soon, by its novelty and popularity, 

 it causes that subject to attract many inquirers, and to be 

 investigated until no more truths are readily discovered in 

 it. Any branch of science, therefore, which has not been 

 much investigated for a long time is, so far, a promising 

 one for research. 



We may extend undeveloped departments of science by 

 several methods, viz. by inventing new apparatus for re- 

 search ; by investigating likely circumstances ; by raising 

 hypotheses and testing them ; by inventing new experiments 

 and making them : by making new observations ; by em- 

 ploying improved means of observation, and by classifying 

 arid studying known truths ; each of which will be sub- 

 divided and treated of in separate chapters. 



Many discoveries have been made by investigating, 

 with the aid of more advanced branches of knowledge, 

 those sections of science which have been left comparatively 

 behind by the progress of other sections; because, as a 

 taan cannot, if his senses are active, traverse an unknown 

 country without seeing new places and perceiving new 



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