10 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



considerable exactness the connection between the frequency 

 of the scintillations and the characters of the spectra, hav- 

 ing regard especially to the four types that have been pro- 

 posed by Secchi. The comparison of his own and Secchi's 

 observations leads him to the conclusion that the stars which 

 have been chosen as showing spectra typical of the first and 

 second classes are also those which have the most frequent 

 scintillations. The typical stars of the fourth class of spec- 

 tra are those whose scintillation is the most feeble. Those 

 stars of the first class which scintillate less than the typical 

 stars are in general distinguished by having less numerous 

 spectral lines. These conclusions he subsequently finds con- 

 firmed by the observations of Huggins and Miller. His es- 

 say concludes by a calculation of the actual differences be- 

 tween the lengths of the routes through the air of the com- 

 ponents of the light of any star, and this leads him to a for- 

 mula which is applicable to the calculation of the relative 

 frequency of the scintillations of various stars at different 

 zenith distances. Bull. Roy. Acad, of Belgium^ 1874, 300. 



THE STRUCTURE OF SOLAR SPOTS. 



The study of the solar spots has very wisely been made a 

 matter of especial attention at the observatory of Allegheny 

 City, Pennsylvania, and Professor Langley, the director of 

 that institution, has the credit of having published the finest 

 photographs and engravings that have ever yet illustrated 

 the subject. From the very cautious wording of a recent 

 communication from him, we gather that among the typical 

 characteristics of the solar phenomena he has observed the 

 following new points : 1. The filaments both of the penumbra 

 and of the umbra are all disposed in curves, which partake of 

 the spiral type, bearing witness to the existence of a force 

 directed toward the centre of the spot; but it does not ap- 

 pear that a uniform direction of rotation prevails, since some 

 of the filaments turn to the one, and some to the other di- 

 rection, while some have a distinct double curvature. 2. The 

 filaments grow progressively brighter toward their extremi- 

 ties, no matter whether they are long enough to reach from 

 the photosphere to the edge of the penumbra, or whether 

 they are shorter than this. 3. lie finds the blackest part of 

 the spot to be intrinsically very bright, and its reddish-brown 



