A. MATHEMATICS AND ASTRONOMY. 13 



not only numerous small cyclones, and even right and left 

 handed whirls in the same spot, but probably currents ascend- 

 ing nearly vertically, while the action of superposed approxi- 

 mately horizontal currents is so general that they must be 

 considered a permanent feature in our study of solar meteor- 

 ology. The outer penumbra is, he, concludes, formed by a 

 rupture. The penumbra is all but wholly made up, as it ap- 

 pears in a first examination, of cloud-like forms, whose struct- 

 ure makes them seem like fagots or sheaves, which Mr. 

 Dawes has compared to bundles of thatch ; while Mr. Lang- 

 ley resolves these sheaves into filaments of extreme tenuity, 

 which he thinks have a tendency to lie in sheets or folds, 

 causing this decrease of brightness. The normal darkness of 

 the outer penumbra is nothing else than the darkness of the 

 gray medium in which the granules float all over the sun, 

 though much deeper tints are here and there found, which 

 sometimes make the penumbra itself resolvable into a ring 

 of little spots. There seems to him no room to doubt that 

 filaments and granules are names for different aspects of the 

 same thing ; that filaments in reality are floating vertically 

 all over the sun, their upper extremities appearing at the sun's 

 surface as granules ; and that in the spots we only see the 

 general structure of the photosphere as if in sections, owing 

 to the filaments beins; here inclined. The average distance 

 from centre to centre of the filaments is less than one second. 

 4 Z>, 1874, VII., 87. 



PHOTOGRAPHS OF THE SOLAR SPECTRUM. 



Dr. Henry Draper, of the Xew York University, communi- 

 cates the highly valuable results obtained by himself in at- 

 tempting to photograph the diffraction spectrum of the solar 

 light. The photographs published by him are of remarkable 

 clearness, and must be considered as an important advance 

 over the spectra that have hitherto been drawn by the hand 

 alone. In the finest maps drawn by hand, such as those of 

 Angstrom, the relative intensity and shading of the lines is 

 but partially represented, and a most laborious and painstak- 

 ing series of observations and calculations is necessary, in 

 order to secure approximately correct positions of the multi- 

 tude of Fraunhofer lines. Thus, for instance, Angstrom, in a 

 certain portion of his spectrum, shows 118 lines, while Dra- 



