14. MOONLIGHT AND ELECTRIC LIGHT. 
pole of the lamp, or 604 paces from the lamp itself. This 
gives the light of the full moon at that hour equal to 
49, 280,000,000, 000, or, in round numbers, 50,000,000, 000, - 
000 times the electric light. 
Two hours later I repeated the measurements, and, as 
might have been expected from the greater altitude of 
the moon, the result was greater, the shadow being equal 
at 55 paces. This gives 58,522,500,000,000, which means 
that this number of electric lights placed 240,000 miles 
away would give as much light as the moon. 
I have called a pace 86 inches, which is quite close to 
the fact. If we call it 34 inches, we shall have to dimin- 
ish the result by 4, leaving in the first case the moonlight 
greater in the ratio of 44,000,000,000,000, and in the sec- 
ond case 52,670,000,000,000. The latter is nearer the true 
ratio when the full moon is in the meridian. To put it 
in another form, one electric light placed on every 225 
square inches of the moon’s surface, considering it a 
plane 2,000 miles in diameter, would light up the earth 
as well as does the full moon. 
The area of a vertical section of the luminous arc is 
very small—one-half inch square I think a very liberal 
estimate. If this is correct, then the luminosity of the 
moon, inch for inch, is 900 to 1,000 times less than that 
of the electric arc. 
To give one arc light of 1,200 candle-power requires 
three-fourths of a horse-power. ‘To illuminate the earth 
from a point as distant as the moon, and to do it as well 
as is now done, would require 39,000,000,000,000 horse- 
power, or 30,000 horse-power for every man, woman and 
child on the globe. 
FEBRUARY 4, 1888—SIXTY-FIRST REGULAR MEETING. 
Le Roy C. Cooley, Ph.D., chairman pro tem., presid- 
ing. 
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