384 Royal Society. 



method the relative areas of the sun uneclipsed at the times of 

 observation were obtained ; and these are seen in column 3 of Table 

 II., the area of the unobscured sun being taken as unity. 



Column 2 gives the results of the photochemical observations 

 made during the eclipse, obtained from the graphical mean, and 

 corrected for variation in the sun's altitude, the total chemical action 

 immediately before first contact being taken as unity. Column 1 

 gives the apparent solar times of observation. 





Table II. 





1. 



2. 



3. 



12 44 



0-915 



0-961 



12 54 



0-876 



0-880 



1 16 



0-686 



0-637 



1 24 



0-555 



0*534 



2 2 



0000 



o-ooo 



2 9 



0-165 



0-127 



2 25 



0-307 



0-338 



2 34 



0-464 



0-498 



2 44 



0-601 



0-602 



2 54 



0-725 



0-736 



3 4 



0-876 



0-861 



From these observations we conclude that the diminution in the 

 total chemical intensity of the sun's light during an eclipse is di- 

 rectly proportional to the magnitude of the obscuration. 



The question of the variation of (1) the direct and (2) the dif- 

 fused radiation is next discussed. On comparing the curve repre- 

 senting the chemical intensity of diffused light with the curve of solar 

 obscuration, it is found that the rate of diminution in chemical action 

 exerted by the diffused light is up to a certain point greater than cor- 

 responds to the portion of eclipsed sun, whilst from this point up to 

 totality the rate of diminution becomes less than corresponds to the 

 progress of the eclipse. The same rapid diminution in the chemical 

 action of the diffused daylight during the early periods of the eclipse 

 was also observed at Jamkandi ; it is doubtless due to the dark body 

 of the moon cutting off the light from the brightly illuminated por- 

 tion of sky lying round the solar disk. 



The results of the observations at Catania are then compared with 

 those made at Moita, near Lisbon, and communicated to the Society 

 in 1870. This comparison shows a striking coincidence between the 

 two sets of observations. In each case it is seen that the relation 

 between solar altitude and total chemical intensity is represented by 

 a straight line, although the Catania observations slightly exceed, by 

 a constant difference, those made at Moita, in conformity with the 

 slight difference in latitude, and with the fact that the former deter- 

 minations were made at a greater elevation above the sea-level. 



The Catania observations further confirm the fact which we for- 

 merly announced, that for altitudes below 50° the amount of che- 



