PEALE.l ON THE COLOR OF WATER. 377 



These experiments render evident several facts: 



First. The color in the specimens is independent of the chemical com- 

 position of the waters. 



Second. It is not dependent upon the quantity of solid ingredients 

 combined in them.* 



Third. The color depends upon the mechanical state of the water, the 

 blues showing- when the water is most free from foreign particles, aud as 

 they increase passing from bUie to green, yellow, and red. 



It is probable that the chemical iugredieuts of the geyser waters are 

 so perfectly dissolved that there is very little matter in a state of sus- 

 pension, aud thus it is that we have such bright coloring in so many of 

 the Yellowstone, Iceland, and other springs. 



We had reached this point in our investigations when we found that 

 the whole subject of the color of water had been fully discussed by va- 

 rious writers. The best resume of the subject probably is found in an 

 article by Prof. John Le Conte in the San Francisco Mining and Scientific 

 Press.t Forbes also gives some interesting information on the subject 

 in Edinburgh Transactions for 1840. Other authorities will be cited in 

 the Bibliographical Appendix. We can give here only the briefest sort 

 of a synopsis. 



It was very early recognized that the color of the sky and the color of 

 pure waters were analogous, and that blue tints were due to reflection, 

 and red ones to transmission of light. 



Leonardo da Vinci (in Traite de la Feinture) ascribes the blueuess of 

 the atmosphere to the effect upon the eye of looking into infinity of space. 

 Euler, in 1762, thought it probable that all particles of air possess a faint 

 bluish tinge, so faint as to be imperceptible unless in a i^rodigious mass, 

 while Muiicke declared the whole thing to be an optical delusion, purely 

 subjective. (See Gehler's Worterbuch, article "Atmosphere.") 



Newton (Optics, Book II) says: 



The blue of the first order, though very faiut and little, may possibly be the color 

 of some substances ; and particularly the azure color of the skies seems to be of this 

 order, for all vapors wheu they begin to coudeuse aud coalesce in small parcels become 

 first of the bigness whereby such must be reflected, before they cuu form c'ouds of 

 other colors. Aud so, this being the tirst color of the fiuest and most transparent 

 skies, in which vapors are not arrived to thijt grossness requisite to reflect other 

 colors — as we find by experience, t 



Tyndall has investigated this subject practically and demonstrated 

 that '• sky-blue maybe produced by exceedingly minute particles of any 

 kind of matter." § 



Sir Isaac Newton, Mariotte, Euler, Sir Humphrey Davy, Count de 

 Maistre, Arago, and others, all thought the azure tints of the deep water 

 of certain lakes and seas was due to the selective reflection of blue rays 

 from the molecules of the liquid itself; while the green and othtr tints 

 exhibited by other waters were thought to be the result of imi)nrities or 



'Another proof of this fact is found in the analyses made by the Society of Public 

 Analysts of England (see the Analyst, of London, vol. vi, February to December, 1K81). 

 In the tables they give the observations on the colors of the waters they have analyzed, 

 and yellow waters are fi'eqnently noted as containing only 5 to 7 grains of solid con- 

 stituents, and waters that are colorless, greenish, or blue, frequently have 35 grains of 

 residue to the gallon. Some waters, also, that are green or blue at certain seasons be- 

 come yellow or brownish at others, probably on account of their sources becouiing 

 turbid from rain. 



tPhysical Studies of Lake Tahoe ; Colors of Sky and Water. San Francisco Mining 

 and Scientific Press, January 1, 1881, to February 12, 1881. 



tClausiiis, of Bonn, thinks the particles should liave a vesicular structure, and says 

 blue skies must h;iv(i fin(;Iy ilivided vapor. Pog. Ann., Ixxvi. 



$0n Chemical Rays and the Structure of the Light of the Sky, in Fragments of 

 Science, p. 258. 



