280 



J. G. Galle's Measurements of the Rainboia. 



May 28. 



June 22. 

 July 1. 



July 24. 



Extreme red 



Red 



Yellow 



Blue 



Extreme red 



Yellow 



Between green and blue. 



Blue 



Violet 



Red 



Green 



Violet 



Red 



Yellow 



Green 



Blue 



Violet 



Distance Reduced to the 

 from the brightest part of 

 sun. the spectrum. 



137 487 



138 1-5 



138 336 



139 59 

 138 160 



138 16-9 



139 8-6 

 139 15-3 

 139 28-1 

 138 8-9 



138 40-8 



139 6-3 



137 38-8 



138 29-6 



138 48-5 



139 1-4 

 139 140 



+ 400 

 +29-0 



00 

 —31-2 

 + 400 



00 

 —21-2 

 —31-2 

 -760 

 +290 

 — 120 

 -76-0 

 + 29-0 



0-0 

 -120 

 —31-2 

 -760 



Distance of the 



brightest portion 



from the sun. 



138 28-7 

 138 30-5 

 138 336 

 138 34-7 

 138 56-0 

 138 16-9 

 138 47-4 

 138 44-1 

 138 12-1 

 138 37-9 

 138 28-8 



137 50-3 



138 7-8 

 138 29-6 

 138 36-5 

 138 30-2 

 137 58-0 



These measurements were executed in the following man- 

 ner: — 1 observed the thne when the inferior portion of the 

 rainbow touched certain terrestrial objects, whose azimuth and 

 height 1 subsequently determined, and then compared with the 

 places of the sun taken from the astronomical Ephemeris for the 

 time in question. The refraction of the sun, the influence of 

 which is small for the portion of the rainbow situated near the 

 horizon, has been neglected. The azimuths of the terrestrial 

 objects were determined by a terrestrial object, whose azimuth 

 was previously known and was tested by comparison with an 

 azimuth of the sun. The reduction to the brightest part of 

 the spectrum has been computed approximatively according 

 to Fraunhofer's figure of the spectrum of the sun, and cannot 

 for several reasons lay claim to any great accuracy. If, with- 

 out any regard to the differences which occur, the mean be 

 taken of the seventeen independent determinations, there is 

 obtained 138° 27'*2, or for the radius of the rainbow, 

 41° 32'-8. 



This agrees exactly with what Prof. Miller of Cambridge* 

 observed on an artificial rainbow, viz. 41° 32'. The theore- 

 tical radius of the rainbow is 41° 27', the geometrical radius 

 41° 53'*9. If in the above measurements we take the colours 

 red to yellow (which are the most definite) and green to violet 

 together, we obtain from the eight measurements by the former 

 colours 41° 29'*9, from the nine measurements by the latter 

 41° 35''3. 



* Phil. Mag. S. 3. vol. xviii. p. 520. 



