356 On the Temperature and Physical Constitution of the Sun. 



"By employing this formula, and starting from the value of 

 t — d which I had obtained at the top of Mont Blanc, the Rev. 

 F. Secchi arrived at the number T = 5335000°*. 



" To control the accuracy of this reasoning, let us apply it to 

 the determination of the temperature of zirconium heated at the 

 oxyhydrogen-lamp. We shall have 



T 



(\0. rtf 



U ^"183960' 

 whence T = 45990°, 



a figure absolutely inadmissible ; for the temperature of a body 

 heated in the oxyhydrogen-flame is at the utmost 2500°." 



In this experiment, therefore, the temperature calculated 

 theoretically, according to the law of proportionality, was about 

 20 times, the actual temperature of the incandescent body. If 

 we had similar experiments at other temperatures of the heated 

 disk of zirconium, we should be in a position approximately to 

 construct the curve according to which the heat-radiation of the 

 incandescent body increases with its temperature. Considering 

 that here not homogeneous, but mixed rays come into operation, 

 the curve would, analogously to the relation found above for the 

 less homogeneous rays of the incandescent platinum wire, conti- 

 nually ascend more rapidly with rising temperature than for 

 homogeneous rays. Apart from the character of an exponential- 

 function, we should in the present case at all events have a right 

 to assume that the ratio of the temperature found by Father 

 Secchi, from the law of proportionality, to the true temperature 

 of the sun's surface is greater than what was found by M. Soret 

 for the ratio of the so calculated temperature of the incandescent 

 zirconium disk to its true temperature. 



If, in accordance with the above values, we take this ratio at 

 20, it will follow that the mean temperature of the sun's surface 

 must at all events be below 267000° C. Of course this does not 

 exclude higher temperatures at greater depths in the body of the 

 sun. According to a correction (already given f) to p. 105 of 

 my previous memoir, at a depth of about -^ of the radius be- 

 neath the surface of the sun a minimum temperature of about a 

 million degrees would result. In conclusion of this memoir I take 

 leave to repeat the general remark made /. c. on determinations 

 of solar temperatures, "that, from the great want of accuracy in the 

 empiric data necessary for these calculations, the values to be pre- 

 liminarily obtained can only be rough approximations, settling 

 rather the order of the temperature-quantities in question than the 

 quantities themselves" 



* The temperature calculated by Father Secchi for the surface of the sun. 

 t Natur der Cometen, p. 490. 



