1824.] Meteorological Society. 465 



at the period of the vapour point, than at almost any other time of 

 the same nights. On other occasions, at the same period of even- 

 ing, the violet and in general the colours of the most refrangi- 

 ble rays were most conspicuous, and the spectrum was more 

 oblongated than ordinarily. Dr. F. at length ascertained that 

 the greater prevalence of the red in the spectrum, uniformly 

 accompanied that state of the atmosphere, when the cirrostratus 

 diffused itself, after sun-set ; whilst the more oblongated spec- 

 trum, with the violet, and most refrangible colours, attended an 

 atmosphere, in which the condensing vapours assumed the form 

 of stratus. He infers from these and other observations, that 

 the changes in the qualities of the diffused vapour in the air 

 must produce great variation in the atmospherical refraction. 

 In the second section of his memoir, he suggests that local cir- 

 cumstances may produce great variation in the mean refractive 

 power of the atmosphere at different places ; and that the dis- 

 cordances in the places assigned to the fixed stars in different 

 catalogues of them may have resulted from such variation. 

 In the third section, entitled ' Of Varieties in the Composition 

 and Nature of the Light of different Stars, considered as still 

 further varying the Effects of Atmospherical Refraction, Reflec- 

 tion, and Dispersion,' Dr. Forster details a number of minute 

 observations upon those varieties ; proceeds to inquire into their 

 causes ; and concludes with an account of some experiments on 

 the decomposition of the light of the moon, the planets, and 

 certain fixed stars. 



A paper by Dr. Forster was also read, " On the great de 

 pression of Temperature which occurred in January, 1820." 



The remarkable depression of temperature related in this 

 paper, took place at Hartfield, in Sussex, to the neighbourhood 

 of which place it appeared to be confined, during the period 

 between sun-set on January 14, and midnight of January 15, 

 1820. At 10 p. in. on the 14th an out-door Fahrenheit's ther- 

 mometer exposed to the NE. was at zero, and at 11 o'clock it 

 indicated — 5°. Sometime between the hours of 1 and 8 a. m. 

 on the loth, it sunk to — 10°, as shewn by a Six's Thermometer. 

 It thence gradually rose, until at midnight on the loth, it 

 attained the elevation of-i-23. A thermometer exposed to the 

 NW, indicated 1° higher in each observation. During this 

 period of excessive cold, the air was calm and clear, a few ill- 

 defined cumuli only were seen on the 15th; the snow which 

 had fallen on the 13th lay on the ground. Dr. F. received only 

 one notice of a distant observation, made at Canterbury, where 

 a Thermometer in-doors indicated 0°; which was also the tem- 

 perature in-doors at Hatfield, on the morning of the 15th. 



Dr. Burney communicated the Results of his Meteorological 

 Journal, for February. 



April 14. — A note was read on certain Phenomena of the 

 New Series, vol. vn. 2 h 



