162 J. Lovering on Velocity of Light and the Sun’s Distance. 
act only by contact, those of hearing and seeing bring the mind — 
into communication with distant objects. The air and the omni- 
present ether supply the delicate and ever ramifying threads 
Se which telegraphic intercourse is maintained with the ear and 
eye. When the origin of the sound or the light is at a large 
Taccncs compared with the yocaty of the acoustic or luminous 
wave, allowance must be made for the time taken by the news 
os an audible or visible event to come to us. ly the vast 
aces of astronomy are commensurable with the great velocity 
of light, and furnish a sufficiently large theatre for a direct 
experiment upon it. But, in stellar astronomy, the magnificence 
of the extent of view so far transcends in magnitude even the 
velocity of light, that the luminous ray, vast as is its velocity) gq 
seems to loiter upon its long wa : 
ence, in astronomy, a distinction exists between the actual 
interval of successive events and the apparent interval. For » — 
example, the first satellite of Jupiter revolves around its primary 
in about 423 hours; and, therefore, enters the shadow of Jupiter, 
months changes back again ; and — the earth is nearest to 
Jupiter, the news of an eclipse reaches us in about 32 minutes, — 
whereas, if the earth is at the Piet distance, 50 nis : 
require 
Consequently, the intervals between successive eclipses, a8 
they exist for our eyes, are variable, being cornea larger and 
sometimes smaller than the real intervals. This regular aa 
the apparent peareae of the eclipses of the same e satellit te, ab 
first attributed to errors of observation, finally condue mgr 
according to Encke’s computations, the quotient, o 
statute miles, is the velocity of light in a secon 
_ The second process which astronomy has su 
ing the velocity of light may be calla, the indirect viens 
a velocity which is commensurable 
ty of light. If two such velocities are co 
inciple of the 
