1883.] The Velocity of Light. 517 
may therefore say, in a general way , the censed velocity of 
light in vacuo will, with regard to any insulated mass within 
the solar system, depend on the radius of the receiver into 
solar distance, indifferent if the inducer of light is in or out 
of the system ; this quotient being subject to change when 
the body is unconstituted, like a comet which expands inde- 
finitely and breaks up in individual masses. 
When we, then, naturally ask, What is solar distance, 
which varies ? what is the radius of the earth ? does it in- 
clude the height of the atmosphere and the mean depth of 
the moving sea, or the mean depth of sea and land raised, 
or neither ? we perceive at once that the first relation given 
is, indeed, a general way, and that the censed velocity of 
light depends essentially on the receiver, without being 
independent from the generator, and its system, ruling all 
other generators and reflectors with regard to our observa- 
tory, the earth. We may comprehend that fully by putting 
to us the further question, How could we receive an image, 
how could we chemically impress it in a photograph, if the 
general, the sectional, and the (in themselves) microcosmical 
molecular masses did not exact on us distinct impressions 
of their individual existence and motions ? 
We would be, indeed, at a loss to make anything of the 
velocity of light if our earth were not so permanently con- 
stituted, for the time being, with regard to the outside world, 
and especially the sun, as our sound eye is, — a colour-blind 
unsound eye combining either exceptional wave-lengths or 
exceptional velocites, and therewith incorrect numbers of 
vibrations. The eye is, in the mean of the indices of re- 
fraction of its parts, identical with that of water ; and salt 
water, the atmosphere of the earth, is that of the eye, which 
so corresponds in its characteristics to sea and land. 
The atmosphere, the real home of light and radiant heat, 
is the distinct stratum at the limit of which begins the action 
of light and radiant heat. 
I showed the air — the elastic, gaseous, dielectric cushion 
round the earth — to be the centrifugal outflow of the sea, 
its 1^333 in mass, as much as the mean centrifugality is of 
the mean attraction of the earth. I showed that the vapour 
ascending from sea and land against the pressing air, turn- 
ing it into atmosphere, is 1-7-59*56 of the mass of the atmo- 
sphere, and that all the water-stuff ascending, and again 
descending as vesicles, drops, crystals, and absorbed vapour, 
at any time suspended in the air being — 
1 4- 59*56 x 2 = 1-7-2978 of the atmosphere, 
