Meteorology. — 'A nou-tanyeul infrnlateral arc". B_v Dr. S. W. 

 Visser. fCoramunicaled by Prof. E. van Evkrdingkn Jr.). 



(Communicated at the meeting of October 27, 1923). 



On 24''' June i923 I saw at the Astronomical Ob.servatory at Leinbaiiff 

 a beautiful halo, which 1 will describe in the following pages. 



Already early in the morning a mock-sun was visible on the right 

 of the snn. Direct measurements of its distance were impossible, as 

 the sun itself was hidden l)y thick clouds. About twelve o'clock a very 

 bright lower tangent arc appeared, which after a few minutes became 

 so intensely luminous as to be visible from time to time through 

 the lower clouds. Soon this arc spread and developed into a com- 

 plete circumscribed halo within wliicii a weak ordinary ring became 

 also visible. I succeeded between 12'' 17'" and 12'' 49'" in taking 

 some 26 measurements of both rings by means of the cloud theo- 

 dolite, mounted at the Observatory expressly for observations of 

 halo's. To these measurements 1 will refer afterwards. In the mean 

 lime I kept a keen lookout for other halo's. Not before 12'' 49'" 

 my effort was rewarded by the apparition of a spot of light on 

 the left below the snn, near the place where (he mayor ring (46°) 

 was to be expected. This spot soon grew more intense and developed 

 into a short, oblique arc. ('oiours (red and green) were visible. On 

 the other side of the sun nothing could he observed, because there 

 the Cu-cloud around the Tangkoehan Prahoe shielded the (Jirrus 

 layer from our vision. 1 now concentrated my full attention on 

 this arc and obtained 12 measurements until li'4"'. Sometimes 

 clouds prevented the observation. Moreover between 12'' 16"i and 

 1" 2"^' fourteen control-observations of the sun were made. Atl''4''i 

 the lower cloud had so much increased, that the measuiements had 

 to be finished. At half past seven in the evening the Ci-St proved 

 to be still present, there was a bright lunar halo, but without any 

 particularities. 



The same halos were seen by M.M. VofiTF, and Rukkn Rapp 



I 



