1870.] Mr. J. N. Lockyer on the recent Eclipse of the Sun. 179 



With a view to the instruction of students in engineering science, he 

 proposes an abridged way of stating the theoretical principles of Mr. Hep- 

 pel's method, considering at the same time that Mr. Heppel's more detailed 

 investigation forms the best model for numerical calculation. 



He then uses Mr. Heppel's improved form of the " Theorem of the three 

 Moments" to test the accuracy of the formulae which he obtained in an- 

 other way, and published in ' A Manual of Civil Engineering,' for the case 

 of a uniform continuous beam with an indefinite number of equal spans, 

 the successive spans being loaded alternately with a uniform fixed load 

 only, and with a uniform travelling load in addition to the fixed load ; and 

 he finds the results of the two methods to agree in every respect. 



V. " Remarks on the recent Eclipse of the Sun as observed in the 

 United States." By J. N. Lockyer, F.R.S. Received December 

 7, 1869. 



By the kindness of Professors Winlock, Morton, and Newton, I have 

 been favoured with photographs, and as yet unpublished accounts, of the 

 results of the recent total eclipse of the sun observed in America. I am 

 anxious, therefore, to take the opportunity afforded by the subject being 

 under discussion, to lay a few remarks thus early before the Royal Society. 



The points which I hoped might be more especially elucidated by this 

 eclipse were as follows : — 



1 . Is it possible to differentiate between the chromosphere and the corona ? 



2. What is the real photographic evidence of the structure of the base 

 of the chromosphere in reference to Mr. W. De La Rue's enlarged photo- 

 graphs of the eclipse of 1860 ? 



3. What is the amount of the obliterating effect of the illumination of 

 our atmosphere on the spectrum of the chromosphere ? 



4. Is there any cooler hydrogen above the prominences? 



5. Can the spectroscope settle the nature of the corona during eclipses ? 



With regard to 1, the evidence is conclusive. The chromosphere, includ- 

 ing a " radiance," as it has been termed by Dr. Gould (the edge of the radi- 

 ance as photographed being strangely like the edge of the chromosphere in 

 places viewed with the open slit), is not to be confounded with the corona. 



On this subject, in a letter to Professor Morton, Dr. B. A. Gould 

 writes : — " An examination of the beautiful photographs made at Burling- 

 ton and Ottumwa by the sections of your party in charge of Professors 

 Mayer and Haines, and a comparison of them with my sketches of the 

 corona, have led me to the conviction that the radiance around the moon 

 in the pictures made during totality is not the corona at all, but is actually 

 the image of what Lockyer has called the chromosphere. 



" This interesting fact is indicated by many different considerations. The 

 directions of maximum radiance do not coincide with those of the great 

 beams of the corona ; they remain constant, while the latter were variable. 



VOL. XVIII. O 



