of solar temperature solely on the result of observations conducted at New York during the summer solstice of 1884.  It will be noticed that the temperature of the large heater is proportionally higher than that of the small heater, a fact showing that the latter, owing to its higher temperature, loses more heat by radiation and convection than the former.  Besides, the rate of cooling of heated bodies increases more rapidly than the augmentation of temperature.

The loss occasioned by the imperfect reflection of the mirrors, as before stated, is 0.235 of the energy transmitted by the direct solar rays acting on the polygonal reflector, hence the temperature which the solar rays are capable of imparting to the large heater will be 200.5 deg. x 1.235 = 247.617 deg.; but the energy of the solar rays acting on the reflector is reduced 0.207 by atmospheric absorption, consequently the ultimate temperature which the sun’s radiant energy is capable of imparting to the heater is 1.207 x 247.617 deg. = 298.87 deg.  F. It is hardly necessary to observe that this temperature (developed by solar radiation diffused fully ten-thousandfold) must be regarded as an actual temperature, since a perfectly transparent atmosphere, and a reflector capable of transmitting the whole energy of the sun’s rays to the heater, would produce the same.

The result of the experimental investigation carried out during the summer solstice of 1884 may be thus briefly stated.  The diffusion of the solar rays acting on the 20 inch heater being in the ratio of 1 to 10,241, the temperature of the solar surface cannot be less than 298.87 deg. x 10,241 = 3,060,727 deg.  F. This underrated computation must be accepted unless it can be shown that the temperature produced by radiant heat is not inversely as the diffusion of the rays.  Physicists who question the existence of such high solar temperature should bear in mind that in consequence of the great attraction of the solar mass, hydrogen on the sun’s surface raised to a temperature of 4,000 deg.  C. will be nearly twice as heavy as hydrogen on the surface of the earth at ordinary atmospheric temperatures; and that, owing to the immense depth of the solar atmosphere, its density would be so enormous at the stated low temperature that the observed rapid movements within the solar envelope could not possibly take place.  It scarcely needs demonstration to prove that extreme tenuity can alone account for the extraordinary velocities recorded by observers of solar phenomena.  But extreme tenuity is incompatible with low temperature and the pressure produced by an atmospheric column probably exceeding 50,000 miles in height subjected to the sun’s powerful attraction, diminished only one-fourth at the stated elevation.  These facts warrant the conclusion that the high temperature established by our investigation is requisite to prevent undue density of the solar atmosphere.