236 GENERAL CONDITIONS OF SCIENTIFIC RESEARCH. 



not carefully considered the difference between discovery 

 and invention. Usually* however, the object of manu- 

 facturers and tradesmen is routine, and entirely opposed 

 to the making of theoretical experiments of any kind. 



In many cases we make a number of experiments, 

 each with a definite object, but do not make a discovery ; 

 for example, fragments of carbon might be immersed in a 

 thousand different liquids in the hope of dissolving it, 

 without our being able to find a solvent ; I have unsuccess- 

 fully immersed it in a great number. Every experienced 

 investigator in physics and chemistry makes numerous 

 experiments, the results of which are consigned to oblivion 

 because they are either negative, inconclusive, or of trivial 

 value. Long periods of time have been occupied in study, 

 books ransacked for information, an endless number of 

 hypotheses invented, rare specimens of nature and art 

 obtained, complicated and expensive apparatuses designed 

 and constructed, rare and valuable substances consumed, 

 but all to no effectual purpose ; nature has either no 

 secret to yield of the expected kind, or we have not 

 employed the proper method of finding it. 



In other cases, we search for one thing and find a 

 totally different one. The planet Pallas was discovered 

 by Dr. Olbers, a physician of Bremen, whilst search- 

 ing for Ceres among the stars of the constellation 

 Virgo. Even in two hours it was observed to have a per- 

 ceptible motion. Bradley also, searching for an annual 

 parallax of the fixed stars, discovered the ' aberration of 

 the fixed stars,' and subsequently, also the nutation (or 

 nodding) of the Earth's axis. ' It appears clear, on con- 

 sideration, that since light and the spectator on the earth 

 are both in motion, the apparent direction of an object 

 will be determined by the composition of these motions. 

 But yet the effect of this composition of motions was (as 



