1882.] On the Recent and Coming Total Solar Eclipses. 291 



terms of the w's and v's. From this equation is deduced the addition- 

 theorem for the functions. 



In §§ 25 and 26 is given the discussion of a particular case of the 

 abo^e, viz., that in which the functions are of the order 2, the fifteen 

 functions being the quotients of all but one of the double theta- 

 functions by that one. The addition-theorem in these functions 

 has already formed the subject of a paper by Cayley in Creile, t. 

 lxxxviii (1878), p. 74. 



IV . " Note on the Recent and Coming Total Solar Eclipses.'' 

 By J. Norman Lockyer, F.R.S. Received November 17, 

 1882. 



The following note has been drawn up in anticipation of the detailed 

 accounts of the work done by me in Egypt on the eclipsed sun of 1882, 

 May 17, which I am preparing to lay before the Royal Society, because 

 as the next total eclipse occurs next May, there is no time to be lost if 

 any attempt is to be made to secure observations, and I am of opinion 

 that such observations are most important. 



I have prefaced the statement of the work done by a reference to 

 the considerations which led me to undertake it, and I have added a 

 scheme of observations which, in the present state of our knowledge 

 is, I think, most likely to produce results of value. 



1. In order to understand the recent change of front in solar research 

 which has followed the introduction of the view of the possible disso- 

 ciation of elementary bodies at solar temperatures, and suggested the 

 later laboratory, and especially the later eclipse ' observations with 

 which we are now chiefly concerned, we must first consider what facts 

 we may expect on the two hypotheses. In this way we can see 

 which hypothesis fits the facts best, and whether there are any 

 inquiries possible during eclipses of a nature to throw light on the 

 question. 



2. On the old hypothesis the construction of the solar atmosphere 

 was imaged as follows : — 



(1.) We have terrestrial elements in the sun's atmosphere. 



(2.) They thin out in the order of vapour density, all being repre- 

 sented in the lower strata, since the solar atmosphere at the lower 

 levels is incompetent to dissociate them. 



(3.) In the lower strata we have especially those of higher atomic 

 weight, all together forming a so-called "reversing layer" by which 

 chiefly the Eraunhofer spectrum is produced. 



3. The new hypothesis necessitates a radical change in the shove 

 views. According to it the three main statements made in para- 

 graph 2 require to be changed as follows : — 



