392 Capt. W. de W. Abney and Dr. T. E. Thorpe. [June 21, 



We have to eliminate jx between these three equations ; the re- 

 sultant between equations of the third and fourth order is given by- 

 Salmon; also the resultant between two quartics, from which we may- 

 deduce the resultant of a quartic and a quintic. The result will be 

 tremendously complicated; but we must remember the number of 

 double tangents to a non-singular quintic is 120, which naturally 

 suggests an equation of the 120th degree, which I apprehend few 

 mathematicians would like to solve. It is impossible, however, to 

 predict the future of analysis. 



I have omitted to take any notice in this paper of the modifications 

 which would be occasioned by double points, hoping, if permitted, to 

 return to the subject. 



I would observe in conclusion that the same method applies to the 

 determination of points of inflexion. Thus in the quartic, taking 

 a, jS, 7, $ for the roots of the equation produced by eliminating between 

 the quartic and a straight line, and putting » == fi = <y, we find it 

 easy to eliminate a. and B and to find two equations which will give 

 the inflexional tangents. 



XIV. "On the Determination of the Photometric Intensity of 

 the Coronal Light during the Solar Eclipse of August 28-29, 

 188(3. Preliminary Notice." By Captain W. DE W. Abney, 

 C.B., RE., F.R.S., and T. E. Thorpe, Ph.D., F.R.S. 

 Received June 21, 1888. 



Attempts to measure the brightness of the corona were made by 

 Pickering in 1870, and by Langley and Smith, independently, in 

 1878, with the result of showing that the amount of emitted light as 

 observed at various eclipses, may vary within comparatively wide 

 limits. These observations have been discussed by Harkness 

 (' Washington Observations for 1876,' Appendix III), and they will be 

 again discussed in the present paper. Combining the observations it 

 appears that the total light of the corona in 1878 was 0*072 of that 

 of a standard candle at 1 foot distance, or 3"8 times that of the full 

 moon, or 0*0000069 that of the sun. It further appears from the 

 photographs that the coronal light varied inversely as the square of 



