J, Lovering on Velocity of Light and the Sun’s Distance. 167 
clock-work, which resolves, in an elegant manner, the problem of uniform 
motion in the particular case in which there is no work to be done. The 
success is so complete that it is my daily experience to launch the mirror 
not allow of the degree of accuracy willingly attributed to it. To meet 
this difficulty, I have introduced into the system of observation a modifi- 
cation which ts simply to a change of the variable. Instead o 
measuring micrometrically the deviation, I adopt for it a definite value in 
advance, suppose seven-tenths of a millimetre, or seven entire parts 
the image; and I seek by experiment to find the distance between the 
mark and the turning mirror necessary to produce this deviation: the 
measures extending over a length of about a metre, the last fractions 
ve a magnitude directly visible, and leave no room for error. 
“ By this means the apparatus has been purged of the principal cause 
of uncertainty: henceforth the results accorded, within the limits of errors 
of observation, and the means are settled in such a way that I am able 
assign confidently the new number which appears to me to express 
nearly the velocity of light in space, viz: 298,000 kilometres in a second 
of mean time.” 
This value, reduced to statute miles, shows that the velocity 
of light is 185,177 miles in a second; which is less by 6836 
miles than the velocity for light usually admitted into science, 
: times greater than the variation between the velocity deduced 
the velocity by Foucault's experiment nor the value of 
tion ¢ 
r of any error roaching to this large discrepancy. 
How is the ‘ee velocity of light to be reconciled with the old 
value of aberration? I have said that aberration establishes 
only the ratio between the velocity of light and the velocity of 
the earth. this ratio cannot be tampered with, and if one 
term of it (the velocity of light) must be diminished by three 
per cent, to suit Foucault's experiment, then we must at the 
same time diminish the other term (the velocity of the earth) 
proportionally; and the old ratio will be ‘preserved, and the 
