DETECTION OF MINUTE OBJECTS. 323 



whilst observing different phenomena, are to be found in 

 treatises on the various sciences. A large amount of 

 in formation respecting the conditions and methods of 

 observing and measuring phenomena relating to astro- 

 nomy, magnetism, hydrography, tides, geography, geo- 

 logy, earthquakes, mineralogy, meteorology, winds, botany, 



thnology, medicine, statistics, &c., is contained in the 

 6 Admiralty Manual of Scientific Inquiry,' by Sir J. F. W. 

 Herschel, Bart., and is well worthy of study by a young 



xperimentalist. Many valuable observations also of a 

 general character on the avoidance and elimination of 

 error in physical observations, are contained in Jevons's 



Principles of Science,' chapter xv. 



As it is an essential condition of successful research, 

 that the investigator should possess clear ideas of his sub- 

 I ect, every person who undertakes a research should be able 

 clearly to describe his observations and conclusions in writ- 

 ing, and there is not, I think, an instance known in modern 

 times of a valuable discovery in science having been lost 

 through a want of power of description or exposition of 

 his observations by a discoverer. 



Sometimes one man observes and another generalizes ; 

 for instance, from the observations made by Tycho re- 

 specting the planet Mars, Kepler educed the path of that 

 planet ; and in a similar manner discovered that all the 

 planets move in ellipses. Dalton based his atomic theory 

 of chemistry upon the results observed by many preceding 

 chemists. 



The cause of original research is greatly aided by the 

 labours of numerous scientific observers, who are continually 

 taking observations and making notes respecting the winds, 

 tides, earthquakes, magnetic changes, the amounts of day- 

 light and of rainfall, and various other meteorological 

 changes ; and the time is fast approaching when nations must 



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