DISCOVERY BY MEANS OF NEW OBSERVATIONS. 563 



CHAPTER LVI. 



DISCOVERY BY MEANS OF ADDITIONAL, NEW, OR IMPROVED 

 OBSERVATIONS. 



THIS also is a most varied and extensive method, because 

 in nearly every department of science a great many addi- 

 tional observations always remain to be made. All our 

 tables of the constants of Nature are more or less incom- 

 plete ; some are exceedingly so, others have not been com- 

 menced. Some observations, such as those of the three 

 terrestrial magnetic elements, require to be made and 

 continued, minute by minute, day by day, year by year, 

 through long periods of time. The specific gravities at 

 ordinary temperatures of a large number of bodies have 

 not yet been determined, and still less of those and other 

 bodies at all temperatures, and under all pressures. Simi- 

 lar remarks may be made of the melting points of solids 

 and the boiling and congealing points of liquids, under all 

 degrees of increased and decreased pressure. The specific 

 heats also of a great number of bodies have not yet been 

 ascertained, and still less have they been determined 

 under every possible variation of pressure and temperature. 

 Precisely similar remarks may be made respecting the 

 incompleteness of our tables of the expansions of solids, 

 liquids, and gases by heat, whilst under different pressures ; 

 of tables of thermic conducting power and electric resist- 

 ance at all temperatures ; also those of transparency to 

 rays of light and heat, chemical rays, and electric and 

 magnetic induction. I need not enumerate more, 

 although a great many remain unmentioned. 



This method, like the previous ones, may be divided 

 into several more special ones, such as, by making additional 



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