C. Bar us — Method for the Observation of Coronas. 279 



sources than the evaporation of smaller particles. In 100 

 seconds about 80 per cent have escaped. The case is much 

 more serious for larger coronas, so that these are characteristic- 

 ally fleeting and must be observed at once. It may not be 

 impossible that rapidity of evaporation itself sets a limit to the 

 largest coronas producible. The nuclei, however, are not all 

 lost, as a rule. They occur, at least in part, as water nuclei 

 and are available for the next coronas, if not removed. 



It follows then that for these cases the method of subsidence 

 is not applicable, as the corona changes totally before measur- 





































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able subsidence is recorded. Hence an instantaneous proce- 

 dure like the former goniometer method or the present 

 method is alone available. 



4. Data. — Omitting the tables, I have constructed in figs. 3 

 and 4 results obtained by the method* of successive equal 

 exhaustion with phosphorus nuclei in dust-free air, leaving out 

 the initial fogs. It is seen at once that large coronal diameters 

 are actually measurable ; a result which was not possible 

 hitherto. Reduced to the goniometer method (figure \c shows 

 the notation) the present results may be written -12xS y = s' for 

 small coronas ; but for large coronas, if 20 is the angular 

 diameter, 3 = 2ff t an 6, s = 2r sin 6 or S = SSs/Vl-syr\ 

 s=-12S/Vl+S 2 /fi 2 ; i?=250 om , r = 30 Cffi . The letters on 

 the curves refer to the colors of the discs and first annuli of 

 the coronas. 



* This Journal, xiii, pp. 81-94, 1902. 



