Manchester Manoirs, Vol. I. (1906), No. 7. ii 



polarisation at different distances from the Sun, and 

 (d) of the decrease in intensity of the total light of the 

 corona with increasing distance from the Sun will be 

 sufficient to determine all our unknown quantities. Even 

 if such measurements are incomplete, we may gain a 

 rough idea of these quantities, and even a solitary observa- 

 tion like that of Mr. Winter during the eclipse of 1871 

 will give some results." 



In an elegant mathematical investigation, complete in 

 all details, Professor Schuster then proceeds to demon- 

 strate these propositions. But the measurements requisite 

 to utilise his results did not immediately follow, probably 

 because the difficulties of obtaining them by visual methods 

 were too great. The gradual introduction of photographic 

 methods, and especially the invention of the " dry-plate," 

 has made them much easier, and at recent eclipses photo- 

 graphs have been obtained which will probably, when 

 suitably measured, give the required information. As 

 yet, however, measures of the polarisation (marked (a) 

 above) have not been carried out, and the complete prob- 

 lem formulated by Professor Schuster has not yet been 

 solved. But extensive measures of class (/'), the total 

 brightness of the corona at different distances from the 

 sun, were made on photographs taken in 1893* and i898-|* 

 (others have been made but are not yet published), and 

 an approximate law was deduced as follows : 



The brightness of the Corona is inversely proportional 

 to the sixth power of the distance from the sun's centre. 



Now, making use of Professor Schuster's paper above 

 referred to, we can immediately deduce from this that the 

 particles must be distributed according to the inverse 4^ 

 power of the distance (see Note I.), and I propose now 



* Proc. Roy. Soc, vol. 66, p. 403. 

 t Froc. Roy. Soc, vol. 68, p. 36. 



