A. MATHEMATICS AND ASTRONOMY. 3 



body. Tlie excess of the polar over the equatorial diameter 

 is, however, a very small quantity, and may be referred either 

 to tides in the photosphere or to the influence of the solar 

 spots themselves. 3Iem. Soc. SpectroscopisU Italiani^ Sept. 9, 

 1872. 



SOLAR SPOTS AND PROTUBERANCES. 



Pere Secchi has lately presented to the French Academy 

 a paper containing some new generalizations on the relations 

 of the solar spots to the protuberances visible with the spec- 

 troscope. He begins by referring to the small number of 

 protuberances during the last four months, especially near 

 the poles of the sun, where they were both few and faint. 

 This diminution in the number of protuberances coincides 

 with a diminution in the number of spots. He is led to the 

 following conclusions respecting the relations between these 

 two phenomena : 



1. The regions of faculse and spots are richest in protuber- 

 ances. 



2. There are two kinds of protuberances: the one thin and 

 feeble, spread out like our thin cirrus clouds in the atmos- 

 phere ; the others, more dense, compact, and brilliant, having 

 a thready structure, and a peculiar optical character. 



3. The spectral analysis of this last class shows that their 

 spectrum is very complicated, and that they contain a num- 

 ber of substances, while the others show only the lines of 

 hydrogen and the line D^. 



A careful study during two consecutive years of observa- 

 tion has convinced Pere Secchi that it is these brilliant and 

 complicated protuberances with which the spots are connect- 

 ed. Two well-established and very general phenomena have 

 confirmed this conclusion. First, although the hydrogen pro- 

 tuberances are seen all around the solar disk, yet the spots 

 are confined to a determinate region, from which it follows 

 that a hydrogenic eruption can not produce a spot. Second, 

 the brilliant eruptions with numerous metallic rays are con- 

 fined to the latitudes of the spots. These two facts led him 

 to suspect that the cause of the spots is connected with the 

 spectral constitution of the protuberances. He therefore 

 carefully noted all the eruptions having this character, which 

 for brevity he calls metallic, and he found that whenever one 



