different kinds of Dry Fogs. 237 



clearly visible as long as it had not risen from 20 to 30 de- 

 grees above the horizon. At Laon, during the day, the light 

 of the sun was of a pale orange colour ; at its setting, it 

 appeared of a fiery red. The moon presented the same 

 appearance. Such is the statement of Cotte. 



Smell of the dry fog of 1783. — The action of this fog on 

 some of our organs was very different from what is observed 

 in aqueous fogs. At Franecker, in Holland, Van Swinden 

 felt a sulphurous odour which excited cough and penetrated 

 into the closest places ; it was particularly sensible on the 

 24th June. At Grceningen not only a sulphurous smell but 

 even a sulphurous taste was perceptible. Marcorelle found 

 it to possess the sharp and stimulating odour of smoke. At 

 Salon it weakened the eyes ; individuals whose chests were 

 delicate experienced disagreeable sensations. Cotte and 

 Toaldo mention nothing of this sort ; but the former, on the 

 testimony of others, relates that in Provence and elsewhere 

 it had a sulphurous, fetid odour, which tickled the eyes. 

 However this may be, the peculiarity in question was not 

 observed in all places. Senebier, Maret, and Cotte state 

 that the fog was without smell, and a great number of ob- 

 servers make no mention of its action on the organs of sight, 

 taste, or smell. 



Meteorological phenomena accompanying the dry fog of 

 1783. — What has been said will, I think, be sufficient to 

 shew that the fog of 1783 was altogether of a special nature, 

 and in no respect formed by aqueous vapour. This opinion 

 will be confirmed by the study of the concomitant phenomena. 

 Its appearance did not take place in analogous circum- 

 stances, but in very varied states of the atmosphere. At 

 Copenhagen it appeared suddenly after a series of clear and 

 warm days ; south-east-south and south-south-west winds 

 succeeded each ',ther in the atmosphere. At Franecker in 

 Holland, Sagan in Silesia, and Peissenberg in Bavaria, the 

 south-west wind prevailed when it was observed for thefirsttime. 

 At Manheim the winds were variable before it first appeared. 

 On the same day it blew successively from west-south-west, 

 \ south-west, and north-west. At Rochelle the south-west pre- 

 vailed for two days w\um it appeared, and the same clay the 



