308 PERSONAL PREPARATION FOR RESEARCH. 



should be acquainted with all the various contrivances 

 which have been employed by earlier investigators for 

 overcoming their difficulties, but also necessary that he 

 should be able to invent new ones readily himself. Such 

 facility of invention is greatly aided by a general know- 

 ledge of all the sciences, because the ideas of the con- 

 trivances by which the questions are tested and difficulties 

 overcome are often derived from some other branch of 

 science different from that of the subject of research ; for 

 instance, the method of detecting the state of vibration of 

 sounding-plates by strewing sand upon them was sug- 

 gested to Chladni by Lichtenberg's experiments of scat- 

 tering powders on an electrified plate of resin. Investi- 

 gators, under such circumstances, often seek the aid of 

 clever mechanics and opticians, who have often in this 

 way, without fee or reward, rendered great and unosten- 

 tatious assistance to the progress of new knowledge; a 

 notable instance of this was the late Carl Becker, of 

 London. In these ways also have arisen, and been gra- 

 dually brought to their present state of perfection, nearly 

 all the experimental apparatus and appliances for produc- 

 ing, detecting, regulating, and measuring all the different 

 substances and forces of nature. 



If the object be to ascertain by experiment a qualita- 

 tive fact, and also its quantitative amount, the former is 

 usually determined first. For instance, in chemical 

 analysis we first make qualitative tests to ascertain what 

 substances are present, and then proceed to find their 

 amounts. In testing a scientific question, either the most 

 conclusive or the most easily-made tests are generally 

 applied the first. Having decided to test a question, and 

 invented a method or experiment for the purpose, it is in 

 many cases a wise course to plan and then arrange or 

 construct a practically workable experiment or apparatus 



