223 M. P. A. Reslhuber on the Decennial Period in the 



The above proposition is proved in a striking manner by the 

 results of the observations of the year 1851, in which an anomaly 

 in the temperature and humidity of the months of May and June 

 is exhibited. 



I am unable to explain the connexion of these phsenomena, 

 but will leave it to other investigators to follow up this highly 

 interesting fact which has resulted from our observations. 



At the end of his paper Dr. Lamont remarks, " that the 

 diurnal deviation of the horizontal intensity is subject to a con- 

 siderable change ; but whether of the same period as that which 

 I have proved to exist in the declination, I am not yet in a posi- 

 tion to pronounce, &c." 



The investigation of the hourly deviation during a day proves 

 that two maxima and two minima occur, and moreover as follows: — 



Between 6** and 7^ p.m. mean stand. 



Between lO'^ and 11^ p.m. a maximum (the least during the 

 day). 



Between 12^^ and 1^ a.m. a minimum (the least during the 

 day, greater than the mean horizontal intensity). 



Between 3'^and4'i A.M. a maximum (the greatest during the day). 



Between 6^ and 7^* a.m. mean stand. 



Between 9^ and 11'^ a.m. a minimum (the greatest during the 

 day, less than the mean horizontal intensity). 



The times of the maxima, minima, and mean magnitude of 

 the horizontal intensity occur at earlier hours in the warm months 

 than in the cold ones. 



The horizontal intensity during the hours of the day is regu- 

 larly smaller, while during the hours of the night it is x'egularly 

 greater than the mean horizontal intensity. 



In order to ascertain whether the horizontal intensity is subject 

 to a periodical alteration, I chose from our observations, which had 

 been made three times a day, those made at S^ a.m. and at S^ 



