INTENSITY OP CORONAL LIGHT DURING THE SOLAR ECLIPSE OF 188G. 379 
mately known, but from trials made subsequently it is probably accurate to witbin 
5 or 6 seconds. 
It will also be observed that both Lieutenant Douglas and Lieutenant Baiens- 
FATHEE continued to read after the Moon and corona were actually obscured by cloud. 
Of course neither of the observers was able to notice the fact of the obscuration with¬ 
out looking up from his instrument. The passage of the cloud was, however, 
readily noticed on the screen of the equatorial photometer, and the time of obscuration 
during the phase of totality was noted. It occurred, as already stated, at about 
1 minute from the calculated end of totality. 
The observations of all these observers show in the clearest manner that the results 
are affected by haze after the first 60 or 70 seconds of totality. Thus, the first six 
readings on the equatorial photometer are fairly concordant, but after 1 minute had 
elapsed the light intensities begin to decrease rapidly. Thus, spots 7 and 10, which 
were considerably nearer to the limb than spots 1 and 4, show a considerably less 
intensity, and the differences are far greater than could be accounted for by any 
possible variation of local intensity in coronal light.'"' Lieutenant Douglas’s readings 
also show a sudden drop at about 60 seconds from the beginning of totality, and they 
continue to decrease steadily and in precisely the same manner as those of Lieutenant 
Baiensfathee. 
This result is indeed what might have been anticipated. It must be remembered 
that the air was practically saturated with moisture ; a slight shower had fallen even 
a few minutes before totality, and the lowering of the temperature consequent on the 
obscuration of the Solar disc would inevitably cause the gradual precipitation of 
moisture from air already charged to saturation. 
If we assume, therefore, that we are justified in regarding the first six observations 
made with the equatorial photometer as valid, we obtain the following eurve as 
showing the photometric intensity of coronal light at varying distances from the Sun’s 
limb expressed in terms of Solar semi-diameters, from Sun centre. 
* The photographs show tliat no such variations in local intensity were present. 
3 c 2 
