[ 307 ] 



VIII. The Dititriliiitiun <>f nine-Violet Light in the Solar Corona on August 30, 

 190;"), as derived from /'/in/ot/ra/i/ix taken (it K<il(ta-es-Senam, Tunisia. 



By L. BECKKK, f'/i.D., Rcyiux I'rofi'ttsor of Astronomy in the University of Glasgow. 



Communicated by the JOINT PERMANENT ECLIPSE COMMITTEE. 

 Received November 27, 1906, Read June 6, Revised August, 1907. 



[PLATE 1.] 

 CONTENTS. 



Section Page 



1. The apparatus ........................... 307 



>. The photographs ........................ 311 



3. The measurements ..................... .312 



4. Kfdui'tions ............................ 313 



5. Correlative distances ........................ 315 



6. Photographs VI. and VII ............ . . ........... 319 



7. Intensity formula .......................... 321 



8. Formula and position angle ...................... 328 



9. Numlier of particles and intensity of light ......... ..".... . 329 



10. Plea for repetition of observations .................... 331 



Appendix I. Diffraction due to screens ................ . 332 



II. Comparison of corona and moon ............... 335 



Tables I.-IV ............................ 337 



Talile I., $ 4 (>), and -^ 7 and S con tain the results derived from the measurements made on 

 .the photographs, viz., equal-intensity curves of the corona and a formula (D) expressing 

 the intensity of the corona as a function of the mean distance from the solar limb of an 

 equal-intensity curve. 



1. The Apparatus. 



The object of my expedition to Kalaa-es-Senam, Tunisia, was to obtain a series of 

 photographs from which might l>e determined the distribution of light in the corona. 



In designing my apparatus, I was led by two considerations: (1) the photographs 

 had to be taken automatically, as I had to work without assistance, (2) standardising 

 of the photographs was to be avoided. All the photographs were therefore taken on 

 the two halves of a whole plate placed end to end and developed in the same tray 

 during the same time. The automatic apparatus gives 10 exposures, and it is 

 governed electrical Iv 1>\ a pendulum dock. I employed two cameras, one with a 



VOL. OCVII. A 420. 2 R 2 19.12.07 



