SUMMARY OF RESULTS AND SUGGESTIONS. 155 



lower depths in which the photospheric clouds are suspended 

 must be separated from the higher levels, to determine the 

 order of succession of the various constituent gases in passing 

 outward from the photosphere through the 800 miles or so of 

 incandescent gases. 



Thus it will be of the greatest interest to learn whether in 

 the lowest depths, where the pressure and temperature are 

 greatest, the emission spectrum becomes more nearly the 

 counterpart of the Fraiinhofer spectrum. Or whether, on the 

 other hand, the dissociating effects of higher temperatures in 

 these regions give rise to a simpler spectrum differing materially 

 from the dark-line spectrum, as well as from the emission 

 spectrum of the higher regions. 



In the photographs recently obtained the bright lines of the 

 Flash represent the integration of the entire 800 miles of depth, 

 and it is not easy to discriminate between high levels and low 

 levels, which may, and probably do, differ very considerably, 

 seeing that the range of temperature and pressure through 

 this depth is likely to be very great. 



At first sight it would seem almost hopeless, with instru- 

 ments of any reasonable dimensions, to perform this detailed 

 analysis of an object subtending so minute an angle ; par- 

 ticularly when it is remembered that under the ordinary 

 conditions of an eclipse the advancing edge of the moon 

 traverses the entire depth of the layer in two or three seconds 

 of time, and only a fraction of a second would be available 

 for photographing the lowest strata. 



I think nevertheless that it will be possible at future eclipses 

 to get fresh evidence bearing on this question, which should 

 show, at any rate, which way the tendency lies with regard to 

 the lowest strata. 



If observing stations were selected, not on the central line of 

 the eclipse, but only a few miles within the north or south 

 limits of totality, it is probable that some important results 

 would be secured. A calculation of the conditions which would 

 obtain at the eclipse of 1900, May 28th, at a station near the 

 limits of the shadow zone, indicates that although totality itself 

 would be a matter of some twenty or thirty seconds only, the 

 duration of the flash spectrum would be many times prolonged, 

 and the covering up and uncovering by the moon would be a 

 very much more deliberate process. 



At a station situated so far from the central line that the 

 duration of totality was reduced to one-third the value it would 

 have on the central line, it would probably be possible to observe 

 the Plash spectrum during the whole time of totality that is, for 

 about thirty seconds at stations in Spain and Portugal. Under 

 these conditions the bright crescent giving the Flash spectrum 

 would be seen to rapidly shift round the limb from second to 



