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series of experiments. It is certainly correct as far as a tempera- 

 ture of 2000° 0. It declares that radiation increases as the 

 square of the absolute temperature, that is the temperature as 

 reckoned from the absolute zero or — 273° C. The readings of 

 the actinometer reduced by this method gives as the resulting 

 effective solar temperature about 18,000° F., a value which 

 Professor Young considers to be more reasonable than any of the 

 earlier estimates. 



7. Other Methods of Determining the Solar Temperature. 

 The problem of the solar temperature has been attacked 

 along yet other lines than those before indicated. Professor 

 Langley has compared sun-light and sun-heat directly, taking 

 equal areas, with the heat and light of the Bessemer converter. 

 Leaving out of account the absorptive action of the atmosphere,' 

 the heat radiation of the Sun per unit area was eighty- seven 

 times that of the molten metal. Others, as ZoUuer and Hirn, 

 have endeavoured to gauge the solar temperature by observations 

 on the velocities of the flames which are to be seen on the limb 

 of the sun in the spectroscope. Velocities of thirty miles a 

 second are common, those of sixty, eighty, and even one hundred 

 miles a second frequent, while phenomenal instances of two 

 hundred and thirty miles a second have been recorded both by 

 Young and Secchi. If these outbursts on the solar surface be, 

 regarded as the result of the escape of powerfully compressed 

 gases, they can be brought under the hand of the mathematician 

 and their temperature gauged with some degree of accuracy. 

 Hirn deduces by this method a temperature of 135,000° F. for 

 the parts of the Sun just above the photosphere, and 8,600,000° F. 

 for the parts below the same level. The late Captain Ericsson 

 constructed at New York an engine for utilizing the direct rays 

 of the Sun, By means of a parabolic reflector they were con- 

 centrated on a cylindrical boiler. Hence steam was generated 

 which was employed to work an engine. A similar machine, 

 devised by M. Mouchot, was to be seen in the gardens of the 

 Trocadero Exhibition at Paris in 1878, which printed a paper 

 aptly styled " Le Soleil." Ericsson considered that by experi- 

 ments which he made with his engine that the solar temperature 

 could not be less than 8,000,000° F. He, however, was a staunch 

 defender of the Newtonian law. Lastly, from spectroscopic 

 indications, Mr. Lockyer is inclined to think that the solar 

 temperature is approximately that of the voltic arc. Great,, 

 then, is the diversity of opinion on this point, even among those 

 who are best qualified to pronounce a judgment. The numbers 

 range from the 3000° F. of the French school of physicists to the 

 18,000,000° of Secchi. What may be the truth it would seem 

 almost impossible to say until a surer knowledge is obtained of 



