714 



height of the sun (27° 45') the lateral arc is tangent to the ring. 

 For all other snns-heights the arc deviates towards tiie outer side. 

 If we allow rotations about I he |)riiici|)a.l axis, iiiiniinum deviations 

 are possible up (o a siuis-height of 80° 50'. According te Exner 

 (f.i. pag. 402) lueasnreinents are lacking. However there exists one 

 by Besson (I.e. png. 71). 23"! April 1908 with a suus-height of53° 

 he saw an iufralateral arc on the left below the sun at a height 

 of 19°, whereas from Bk.wais's (lieory a heigiit of 18° 57' would 

 follow. 



This case bears some resemblance to that of Lembang. "Three 

 uiiiiules afterwards" Besson writes "the ring of 22° and the circum- 

 scribed halo appeared, complete bul scarcely visible". In both 

 ol)servalions the same foiins of halo's appear. ') 



For the measurements at Lembang as a rule the red of the arc 

 was vised at. Once green was measured. Two times the left- and 

 righthand ends of the red were determined. 



The readings and some distances and angles calculated from these 

 have been enteied in the following table. 



The observations 5 and 9 refer to the lefthand end. 6 and 8 to 



1) See also: E. van Evebdinskn. Halo's in April, Heme! en Dampkring 21. 

 1923, p. 216, 217. 



