Physical Constitution of the Sun. 323 



increases from the surface towards the centre, the specific gravity 

 of the layer of division must necessarily be smaller than that of 

 the mean specific gravity of the sun. If we assume that the 

 highest limit of specific gravity of this layer is the mean specific 

 gravity of the sun, we shall have to assume that all the deeper- 

 lying layers, and therefore the still deeper-lying gaseous layer, 

 have the same temperature. But then the interior of the sun 

 would not consist of a gas, but of an incompressible liquid. All 

 these deductions are, it will be seen, necessary consequences of 

 the supposition that the specific gravity a of the compressed 

 gases issuing in these eruptive discharges reaches its maximum 

 limit, viz. that of the mean specific gravity of the sun. 



In this case, however, the first supposition changes into the 

 second, according to which the sun consists of an incompressible 

 liquid, near the surface of which local aggregations of masses of 

 glowing hydrogen occur ; and these burst forth when a sufficient 

 difference of pressure presents itself, giving rise to the pheno- 

 mena of eruptive protuberances. 



However small these spaces may in certain cases be supposed 

 to be, the specific gravity of the enclosed mass of gas cannot be 

 taken to be greater than that of the surrounding liquid ; other- 

 wise the compressed gas would sink into the interior of the sun. 

 The specific gravity of the sun is, according to the newest 

 results, 1*46. If we insert this value for cr in equation (V.), and 

 for a the number 40690, and for h the value 8" in metres, we 

 obtain the following limiting values for ^ = 0*500 metre and 

 ^=0*050 metre: — 



for ^ = 0-500, *= 29500°; and for j^= 0-050, /= 26000° 



or a mean value of t = 27700° as the absolute temperature of 

 the solar atmosphere. 



If equation (5) be differentiated according to /, the differential 



quotient -7- becomes negative — that is, cr diminishes for increas- 

 ing values of t. Hence it follows that the above values of t are 

 minimum values. 



With the mean value of t for the temperature of the sun's 

 atmosphere the value iov p h of 0'180 metre is obtained. These 

 values are used in the following calculations. 



It may be remarked that the high values obtained for these 

 temperatures are about eight times that given by Bunsen* for 

 that of the oxyhydrogen-flame, and that iron must exist in the 

 solar atmosphere in a permanently gaseous state. 



From formula (I.) the value of the internal temperature U is 

 found, when £=27700°, to be *,-= 68400°. If we substitute 



* Pogg. Ann. vol. cxxxi. p. 172. 



