44 Selim Lemsteöm. 



The place where they Avere made, consisted of a potato fleld situated 0,8 m 

 above lake Wanjärvi, at a distance of about 70 m from it [See note VIII]. 



A doser examination of the table shows us that température falls more 

 slowly during an autumn-night than during a summer-night. 



Taking, for example, the 21"' August, we find that the température 



had fallen about 1" per hour, but that after this time, according to the minimum- 

 thermometer, which was observed the following morning, it had not fallen 

 lower than 5'',3, during the whole night. Suppose this degree of température 

 to hâve occurred at 4,5 a. m. or shortly before sunrise, the falling will amount 

 to SV in 6 hours, or O^jSS per hour. 



The 27"" August passed in the same way, and also the 30"', when the 

 température shortly after sunset went down 



from 7,25 p. m. 7",i 

 to 10,15 „ 4",+ 



or about 1" per hour. 



The next morning the minimum-thermometer showed that the lowest tem- 

 pérature had been 3°, 7 and that, after that time, the température began to 

 rise, showing already at 5, o a. m. 6",+. 



During the 23-24"' September the température on the ground remained 

 constant all night, but feil 0,7 m above it from 9,5ü p. m. on the 23"", when 

 it was l'',2, 



to 3,45 a. m. on the 24'^'', when it was — 0",4, and continued to fall un- 

 til 6,10 a. m., when it was — 1°,8. 



The curions circumstances prevailing that night and which will be more 

 closely treated below, will pro ve, that this fall of température cannot be attri- 

 buted to the radiation from the ground alone. The observations give no cause 

 to conclude a more rapid fall of température in the morning. Such a fall is, 

 in general, to be expected w^hen the ontward circumstances prevailing at 

 the time, are of a certain character, which will be more closely pointed out 

 below. 



As the observations made in the evening of September 23'''' and in the 

 morning of 24"", serve to illustate the causes of a peculiar kind of frosts, be- 

 sides, giving scope for other conclusions, they will be given separately here 

 in the order in which they were executed. 



