this connection that Lummer and Pringsheim" have found these laws in agreement at 2300° abs.

If we can assume that the Wien-Planck and the Stefan-Boltzmann relations continue to hold good for thermodynamic radiation at these high temperatures, it would seem, in view of the above fact, that the phenomena of luminescence plays no very important part in the radiation from the positive pole of the electric arc; for, if so, it might be expected to lead to higher values in the estimates based on the photometric methods than would be found by methods dependent on total radiation.

An examination of the available estimates of the temperature of the sun, made by methods based on the photometric intensity, seem to indicate that these methods lead to higher values than those based on

the energy of total radiation. Thus, using the former method,

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Le Chatelier' finds 7900° abs. The estimates, based on total radiation and on the position of the wave length of maximum energy in the solar spectrum, lead to values in the neighborhood of 5500° to 6000 absolute. If this difference in the methods really exists, it would at least suggest the presence of luminescent radiation. It would also be of interest in this connection to use the photometric method with green and blue, in addition to red radiation, to see if the former led to higher values, as might be expected if luminescence played an important rôle.

a Lummer and Pringsheim: Verh. Deutschen Phys. Ges. (5) I, p. 3; 1903. Le Chatelier: C. R., 114, p. 737; 1892.

As Le Chatelier's determination of the arc temperature is probably several hundred degrees high, his value of the effective temperature of the sun should be lowered.

d Day and Van Ostrand: Astrophys. J. 19, p. 39; 1904.

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