A. W. Wright—Polariscopic Observations of Comet c, 1881. 373 
11 each number is the percentage of polarization derived from 
ten separate measurements; column III gives the mean of these 
or. each evening; in column IV are given the angles of inci- 
dence of the solar rays. These are obtained by graphic inter- 
polation from a curve representing the angles calculated from 
the ephemeris of H. Oppenheim,* for the dates there given. 
} a Ill. IV. 
13°4 : °, 
Aug. 20, 8 30™ to 95 30™, P.M. 14-9 13°8 54°°6 
h 11°0 2 : °, 
Aug. 22, 8 30™ to 92 15™, P. M. 9-7 10°3 55°'6 
ie : 10°5 ; ‘i 
ug. 25, 8h 30™ to gh, P. M. 11 110 55°2 
Aug. 27, 8% 30™ to gh, P.M. [16-3] [6's] 54°] 
The percentage for August 27 was obtained from two set- 
tings of the plates only, and is entitled to less confidence than 
the others. That the polarization was really increasing, how- 
ever, was easily recognized by the appearance of the bands, 
and their relative brightness in the two positions of the glass 
plates. After this date the condition of the sky was not at any 
time such as to render further determinations possible 
in general to the law of variation for a gaseous medium, where 
the curve representing it has the maximum at the incidence of 
* Astron, Nachr., No. 2388, p. 190, + Loc. cit. 
