SOUTHERN GALIFORNIA ACADEMY OF SCIENCES 63 
data: namely, the amount of heat received on a square foot of 
surface in’ one minute—taking as a unite of heat, the heat 
which raises a pound of water one degree Fahrenheit. 
He found that the heat received at the Earth from the Sun 
in the zenith, is suffiicient to melt an inch thick layer of ice in 
two hours and thirteen minutes. That is, if an inch thick shell 
of ice encompassed the Sun, distant from its center in all di- 
rections ninety-three million miles that immense, remote ice 
shell would all be melted in two hours and thirteen minutes. 
With Young, our highest authority on solar facts, fancy 
such an inch thick shell of ice kept imtact and drawn inward 
toward the sun, all the while containing ithe same quanity of 
ice, becoming thicker as it lessens in Sze. When it touches 
the Sun’s surface its thickness will exceed one mile. 
That vast, solid glacier, embracing the Sun, at every point 
over one mile high, would all be melted by ‘the Sun’s heat in 
two hours and thirteen mimutes. It would melt a layer about 
forty feet thick each minute! 
All honor to Herschel’s coneeption and achievement. His 
method was perfect, but not his instruments. Better means 
now prove that the Sun radiates from its entire surface in one 
minute enough heat to melt encasing ice sixty-four feet thick! 
Temperature of the Sun. 
Within experimental limits Stephen’s thermal law holds, 
namely that the rate of heat. radiation is as the fourth power of 
the absolute temperature. Assuming it to hold universally, 
this law and the known rate of the Sun’s radiation—500 thous- 
and units of heat per minute from each square foot of solar 
surface~give as the Sun’s surface temperature 12,0009 F, 
about sixty times the temperature of boiling water! 
With much more certanity, a lower limit to the Sun’s sur- 
face temperature has been found experimentally. Scheiner by 
ingenius use of the spectroscope, comparing lines of the solar 
spectrum with certain lines of magnesium, proved that the 
photosphere is hotter than the eleetrie are—that is, that its 
temperature is certainly above 7000" F. So also, the heat at 
the focus of a powerful len has furnished a lower limit in a 
very realistic way. 
The Sun’s rays received on a lens or burning-elass are con- 
verged to its foeus, producing at that point a high temperature. 
A point out im space to which the Sun’s rays naturally converge 
at an angle equal to the focusing angle of the lens, may be 
termed the space-point of equal temperature. Its distance from 
the Sun is easily found, for the ratio of that distance to the 
