that if a suitable thermometer could be projected into
space it would give a reading of -273 deg.. On the contrary, not being a
transparent and diathermanous body, it would absorb radiation from the
sun and other stars, and would thus become warmed. Professor J. H.
Poynting ("Radiation in the Solar System," _Phil. Trans._, A, 1903, 202,
p. 525) showed that as regards bodies in the solar system the effects of
radiation from the stars are negligible, and calculated that by solar
radiation alone a small absorbing sphere at the distance of Mercury from
the sun would have its temperature raised to 483 deg. Abs. (210 deg. C),
at the distance of Venus to 358 deg. Abs. (85 deg. C), of the earth to
300 deg. Abs. (27 deg. C), of Mars to 243 deg. Abs. (-30 deg. C), and of
Neptune to only 54 deg. Abs. (-219 deg. C.). The French physicists of
the early part of the 19th century held a different view, and rejected
the hypothesis of the absolute cold of space. Fourier, for instance,
postulated a fundamental temperature of space as necessary for the
explanation of the heat-effects observed on the surface of the earth,
and estimated that in the interplanetary regions it was little less than
that of the terrestrial poles and below the freezing-point of mercury,
though it was different in other parts of space (_Ann. chim. phys._,
1824, 27, pp. 141, 150). C. S. M. Pouillet, again, calculated the
temperature of interplanetary space as -142 deg. C. (_Comptes rendus_,
1838, 7, p. 61), and Sir John Herschel as -150 deg. (_Ency. Brit._, 8th
ed., art. "Meteorology," p. 643).

To attain the absolute zero in the laboratory, that is, to deprive a
substance entirely of its heat, is a thermodynamical impossibility, and
the most that the physicist can hope for is an indefinitely close
approach to that point. The lowest steady temperature obtainable by the
exhaustion of liquid hydrogen is about -262 deg. C. (11 deg. Abs.), and
the liquefaction of helium by Professor Kamerlingh Onnes in 1908 yielded
a liquid having a boiling-point of about 4.3 deg. Abs., which on
exhaustion must bring us to within about 2-1/2 degrees of the absolute
zero. (See LIQUID GASES.)

For a "cold," in the medical sense, see CATARRH and Respiratory
System: _Pathology_.

COLDEN, CADWALLADER (1688-1776), American physician and colonial
official, was born at Duns, Scotland, on the 17th of February 1688. He
graduated at the university of Edinburgh in 1705, spent three yea