A. MATHEMATICS AND ASTRONOMY. 19 



and concludes th.it, in the fluctuations of the observed values 

 of the horizontal and vertical diameters of the sun, no de- 

 pendence upon the variations of spots can be perceived. 

 Monthly Notices Roy. Ast. Soc, 1873, XXXIV., 22. 



THE TEMPERATURE OF THE SUX. 



The latest investigation on the temperature of the sun, by 

 Father Secchi, has been recently published, and he concludes 

 tl at the lowest limit of this temperature must be about 

 133,000 Centigrade. He lias arrived at this determination 

 by a comparison of the solar radiation and that of the elec- 

 tric light. He has employed the same apparatus (the thermo- 

 heliometer) described in his well-known work on the sun. 

 The temperature produced by solar radiation was observed 

 at Rome, about noon, on several days in July, and was de- 

 termined to be 3G^ times that of the carbon points of his 

 electric light. Both Secchi and Hirn agree that the temper- 

 ature of solar radiation may depend either solely on the su- 

 perficial stratum of the sun, or on a considerable thickness 

 of its substance, according as this latter is opaque or trans- 

 parent. Hirn concludes that if the transparence were nearly 

 perfect, the solar temperature might well be only a few 

 thousand degrees ; but various phenomena, among them the 

 observations of Professor Lano-lev, of Pittsburgh on the cross- 

 ing of the currents of the photosphere, show that the solar 

 surface is essentially opaque, and certainly at the best is 

 not completely transparent. The very high temperature of 

 130,000 to 170,000, above given, is, therefore, not inadmis- 

 sible, but may be looked upon as at least giving a lower limit 

 to the true value of the temperature of the sun. 7 A, 47, 

 394. 



OX SOLAR RADIATION. 



In regard to the use of thermometers for determining the 

 intensity of solar radiation, Mr. Stow has recently been mak- 

 ing a number of observations, the report on which is about 

 to be published. He expresses his own opinion, in a prelim- 

 inary manner, as follows : "Looking at the subject attentive- 

 ly, there are three different objects which meteorologists 

 may propose to themselves in attempting to measure the 

 sun's heat. The first is the measurement of the intensity of 



