i88 3 J 
57i 
The Velocity of Light . 
The velocity of light with regard to the individual earth 
depends therefore on the quantities and qualities of the 
medium atmosphere, themselves subject to the interaction 
of earth and sun. 
So little as light is heat, but both are intimately con- 
nected, so little are light and radiant heat identical : light 
therefore ends where we cease to see it in the speCtrum ; no 
thermometer, thermopile, or bolometer is made for it, but 
the eye is. Absence of light begins on the side of the red, 
where the uniform motion gets deviated, delayed, and 
divided by resistance, when the rotatory tendency of mole- 
cules exceeds that of vibratory propagation of transport or 
or orbital motion in the mass ; darkness begins on the side 
of the violet, when the solar opposition and impulse against 
terrestrian and molecular centrifugality is so diminished by 
interposition in and deviation from its straight path, and the 
number of molecular vibrations so increased and the length 
of waves so reduced, that an altered polar aCtion introduces 
new molecular combinations. 
Any more or less diaphanous substance, or made diapha- 
nous by change of state, being a distinct medium, produces 
a speCtrum of its own, according to its gaseous, liquid, or 
solid state, the aggregational and the internal state of its 
molecules, and its changes in temperature, pressure, and 
form. Any such medium introduced into the atmosphere 
therefore modifies the atmospheric speCtrum ; but the atmo- 
sphere, air and water-stuff, is the true medium of light, 
the instrument formed by earth and sun for their use, and 
all other substances coming and going in it in small quanti- 
ties are instruments that have to submit and fit in the 
atmospheric orchestra and its pitch, and to equalise and 
absorb their characteristics in the unity of harmony. The 
solar speCtrum is the atmospheric speCtrum, all kinds of 
molecules being there and here represented. 
It follows from day and night, from the undulatory theory, 
that the scale of wave-lengths in this speCtrum cannot sur- 
pass the scale 1 : 1—2 = 2 : 1, from darkness to darkness. 
Angstrom found the wave-lengths of line A 760*4 millionth 
of a millimetre, and of H 2 393*3, which gives for a metre 
for A 1,315,100, and for H 2 2,542,500 lengths. 
“ Not only the darkness of A and B, but their appearance 
depends on the relative position of the sun, on his being 
near the horizon ” ; “ they are called entirely atmospheric.” 
So it is with H 2 ; A will be more prominent in the morning, 
H 2 in the evening. “ Janssen has even succeeded in pro- 
ducing, by absorption of vapour of water, black rays near 
2 P 2 
