156 



KNOWLEDGE 



[July 1, 1898. 



being to photograph the changes in the spectrum due to 

 the " reversing layer," and also to secure photographs of 

 the 1474 K line for the purpose of determining the question 

 of the rotation of the corona. The two smaller photographic 

 telescopes, together with the spectroscopes, were all carried 

 on the same mounting, which was practically one of the 

 English form, and may be seen in the centre of the photo- 

 graph just beyond the base of the great telescope. 



Speaking generally , the recent eclipse has been specially re- 

 markable for two classes of photographs — those of the corona 

 on a large scale, ami those of the spectrum of the " flash." 

 Mr. Evershed's photographs are well entitled to stand as re- 

 presentatives of the latter, and we may well take Prof. Camp- 

 bell's beautiful picture as a representative of the former. 



These 





Prof. Camjibell's Obserrmg Station at 

 January 



scale photo- 

 graphs were 

 undertaken a t 

 three stations : 

 at Sahdol, where 

 Prof. Michie 

 Smith used a 

 forty- foot camera 

 like Prof. Camp- 

 l)ell's, rigidly 

 fixed and pointed 

 directly to the 

 sun ; and where 

 the Astronomer 

 Royal used 

 the nine-inch 

 Thompson pho- 

 tographic lens of 

 Greenwich Ob- 

 servatory, in 

 combina t ion 

 withaDallmeyer 

 telephoto lens, 

 by which the im- 

 age was enlarged 

 from a diameter 

 of one inch to 

 one of four. 



This, the most powerful photographic instrument in use in 

 the echpse, was fed by a ccclostat. Prof. Copeland, at 

 Goghli, also used a lens of forty-foot focus, but mounted 

 it horizontally and used a heliostat. There was, therefore, 

 a wide range of method, though the resulting photographs 

 were approximately on the same scale. 



In the March Number of Knowledge we pointed out 

 that of coronit, as seen directly, there were three well- 

 marked types. In the May Number we drew attention to 

 the correspondence between long-exposed photographs 

 and the visual appearance. In the present case we wish 

 rather to speak of those details of the lower corona which 

 are probably common to all types, and which are very 

 well exemplified in the present photographs. 



1. Pdliir Bays. — These are seen with exceptional clear- 

 ness in many of the photographs of the late eclipse. They 

 seem to spring almost from an actual point on the sun's 

 surface, and to diverge nearly in straight lines, but with 

 a tendency on the part of those diverging the most widely 

 to curve over towards the equator. Generally speaking 

 the corona gives the idea of a flat picture, not of a body 

 based upon a sphere and having depth as well as extension. 

 But, on the present occasion at any rate, the polar rays 

 seem distinctly placed at difierent distances, and some 

 appear foreshortened while others are seen in their full 

 length. It might be added here that Prof. Campbell's 



photograph shows better than any other with which we 

 are acquainted a pretty little group of prominences near 

 the north pole. 



2. Ile-cntering Curves, — A prominent feature of the 1893 

 eclipse I at sunspot maximum) was the number of in- 

 stances in which a bright group of prominences was arched 

 over by a bright coronal line which formed a complete 

 bridge above it. Not only so, but the coronal structure 

 was distinctly less brilliant below this arch and round the 

 prominence. The prominences appeared, therefore, as if 

 they were covered by glass shades or bell jars, and it 

 would seem as if the prominence exercised some repulsive 

 efifect upon the corona matter. In some cases arch suc- 

 ceeded arch, the prominence group being enclosed beneath 



a succession of 



^^ more or less per- 



• feet re-entering 



curves. 



3 . Radial 

 Linrs. -The 

 great streamers 

 or extensions of 

 the outer corona 

 are usually bor- 

 dered by bright 

 lines of a very 

 peculiar and 

 characteristic 

 form, lines of 

 double curvature 

 which give those 

 streamers their 

 well-known 

 lobed or leaflike 

 shape. These 

 lines often start 

 almost tangenti- 

 ally to the disc. 

 In the present 

 echpse there are 

 several marked 

 cases in which 

 these curves, 

 starting thus tangentially, and curving round almost 

 concentrically with the sun, become caught by a vehement 

 repulsive force, and are swept outward in a straight line 

 radial to the sun. The triple ray in the north-west is, 

 perhaps, the most striking instance of this. 



Jeur, India, during the Total Eclipse of 

 22nd, 1898. 



Notices of ISoolts. 



Thermo - Gtoyrapkical Studies. By C. L. Madsen. 

 (Williams & Norgate.) This general exposition of the 

 analytical method applied to researches on temperature 

 and climate, gained for the author both an honourable 

 mention and a sUver medal in the competition for the 

 Hodgkins prizes offered by the Smithsonian Institution, 

 Washington, in 1898. Equations are deduced for the 

 determination of the normal mean yearly temperature of 

 the parallels, of the mean yearly temperature of places 

 of given geographical latitude and longitude, and of 

 the yearly movement in the temperature of places in 

 the northern temperate and polar zone. A comparison is 

 instituted between the actually observed and calculated 

 mean yearly and monthly temperature of one hundred and 

 twelve places situated in the middle Atlantic zones of the 

 northern hemisphere. There is, in addition, a mass of 

 observations and data dealing with other branches of this 



