1818,] and their Effects. 369 



they were all followed by, rain, in some instances in less than 

 four hours after disappearing. 



On the 23d, from 40' till 55' after five, p.m., a double solar 

 rainbow appeared to the east, when the sun was within two or 

 three degrees of the western horizon, and measured as follows : 



Diameter of the exterior semicircle 84° 30' 00' 



Distance of the interior from the exterior bow at\ o 90 qq 



the north side j 



Distance of ditto from ditto at the south side . . 8 22 30 



Greatest diameter of the exterior semicircle .... 101 15 00 



This measurement of the rainbow is as wide as it can be within 

 9', according to the most accurate calculation ; it was of longer 

 duration, and the finest in colours that I ever remember to have 

 seen ; and the sun was so favourably situated as to make it the 

 largest in extent. 



Sept. 25. — Fine coloured parhelia appeared this morning at 

 intervals from 50 minutes past seven till five minutes past eight 

 o'clock, on an attenuated Cirrostratus cloud from the southward. 

 At eight, the sun's altitude from the horizon was 19° 4' 40", and 

 each parhelion was 23° 30' distant from, and parallel with, the 

 real sun, making their altitudes equal with the luminary, and 

 the halo in which tbey were situated, and which was very con- 

 spicuous, 47° in horizontal diameter. Each parhelion disap- 

 peared three times, and their formation on re-appearing was 

 more simple than that of the parhelia which I attempted to 

 describe in page 235 of the last number of the Annals : the 

 colours, however, were similar, but the mock-suns smaller, viz. 

 a little larger than the apparent size of the sun's disc. 



State of the Wind, Clouds, and Instruments, at Eight o'Clock. — 

 Wind, due south. Attenuated Cirrostratus, gradually increasing 

 in extent and density, through which the sun shone faintly, 

 and some Cirrus in the zenith. Height of the barometer 29-60 

 inches, and of the thermometer 55°. De Luc's whalebone hy- 

 grometer 75°, there having been a copious deposition of dew 

 upon this instrument till after sun -rise. These, as well as the 

 last parhelia, were followed by a sinking barometer ; the sky 

 was overcast by two, p.m. and rain came on at four. 



26. — About eight minutes before eight, a. m. three coloured 

 parhelia appeared on a thin Cirrostratus that was passing very 

 slowly in a north-west direction from this place ; the sun's altitude 

 at the same time being 18° above the horizon, and the halo, m 

 which the parhelia were situated, 45° 10' in horizontal diameter 

 to the outside of the colours. 



The two parhelia parallel with the sun, were each 22° 35', and 

 the upper parhelion nearly 23° distant from the centre of his disc ; 

 the latter was formed by the intersection of part of another halo 

 at the top of the perfect one, and the parhelion at the point of 



Vol. XII. N°V. 2 A 



