A. MATHEMATICS AND ASTRONOMY. 15 



CHANGES IX THE SOLAR SPOTS. 



The latest communication from Messrs. De La Rue, Stewart, 

 and Loewy, in reference to their joint work on the solar spots, 

 communicates an entirely unexpected discovery, to the effect 

 that, during periods of great disturbance, there is a tend- 

 ency in the spots to change alternately from the northern 

 to the southern hemisphere, and vice versa, the period of such 

 change being about 25 days. On the other hand, it is only 

 when the solar disturbance is inconsiderable that the spots 

 do not present any such systematic oscillation. Connecting 

 this generalization with the previous discoveries of Carring- 

 ton, as well as with their own, they conclude that it is de- 

 monstrable that outbreaks probably occur in pairs, at oppo- 

 site ends of the same solar diameter, at an interval of twelve 

 or thirteen days. Pr. Boy. Soc, 1873, 401. 



SOLAR SPOTS AND SOLAR REFRACTION. 



Lohse, of Bothcamp, has communicated to the Astronom- 

 ische Nachrichten, a valuable memoir, both theoretical and 

 observational, on the determination of the depth of the sun- 

 spots and the amount of solar refraction. He has attempted 

 to add something to our knowledge of this subject by a se- 

 ries of micrometric measures made upon the solar spots at va- 

 rious distances from the limb of the sun, following out the 

 idea published just one hundred years ago by Wilson, of 

 England, and which may be expressed as follows: "By meas- 

 uring the distance of the edge of the spot from the solar limb 

 at the moment when the side of the umbra is just hid or be j 

 gins first to come in view, the inclination or declivity of the 

 spot may in some measure be obtained." But few opportu- 

 nities have offered themselves to Lohse to make such meas- 

 ures relating to this phenomenon; and the first result to 

 which he has been led has been the development of a system- 

 atic discordance that can not possibly be referred to errors of 

 observation, but can be explained as the result of refraction 

 in the solar atmosphere. A discussion of observations made 

 with reference to the same point by Secchi, leads also to a 

 decision in favor of the assumption of a perceptible refrac- 

 tion even in the upper strata of the solar atmosphere. As- 

 tron. Nach.) LXXXIIL, 1 1 4. 



