1893.] of Observations of Air Temperature and Pressure. 69 



The second component has two clearly marked maxima about the 

 time of the equinoxes, and a principal minimum at midsummer. 



The component of the third order varies in a converse manner, 

 having two well-marked minima at the equinoxes, with a principal 

 maximum at midsummer. 



The component of the fourth order appears to combine the cha- 

 racters of the two previous ones, having two maxima about the time 

 of the equinoxes, and a principal minimum in the winter. 



The following empirical formulee give close approximations to the 

 values of P 2 and P 3 : 



P 2 = 1-08 + 0-20 cos (A, + 126°) + 0'41 cos (2\— 2°), 

 P 3 = 0-42 -f-0'16 cos + 260°) +0-10 cos (2\— 172°), 



in which A, is the sun's longitude. 



The mean value of ft for the first component is 214°, correspond- 

 ing to 2 h. 26 m. p.m., the variation due to season being 12° or 48 m. 

 of time, by which the maximum is earlier in summer than in winter. 



In the second order the first maximum in June is 24°, or 1 h. 20 m. 

 earlier than in January. 



In the third order the difference in the same direction is 63°, or 

 A h. 12 m. of time. 



In the fourth order, there is some doubt as to the manner in 

 which the change of epoch of the summer and winter maxima is 

 brought about. From March, when the first maximum occurs about 

 60° after midnight, or 4 a.m., there is a continued retrogression till 

 June, when the maximum is at 16° after midnight, or 1 h. 4 m. a.m. 

 This is followed by a progression from June till October, when the 

 maximum again occurs at about 60°, or 4 a.m. 



In passing from October to November, a sudden change takes place 

 by which the maximum is established at about 10° after midnight. 

 There is a like sudden change between January and February in 

 the opposite direction, which again brings the maximum to 60* 

 after midnight. From the component in November and February 

 being very small, it is not improbable that these sudden changes 

 may coincide with the component becoming zero. 



Remembering that the fourth component includes four series of 

 undulations, the most probable explanation of these changes is to be 

 found in a change of the position of these undulations, during which, 

 between January and February, the first recedes, and its place is 

 taken by the second, which leads to sudden appearance of a maxi- 

 mum about 60°, or 4 a.m. A similar change between October and 

 November in an opposite direction would introduce the maximum at 

 10° after midnight. 



In the summer months (May, June, and July ) the temperature 

 curve during the day hours, from 8 a.m. to 8 p.m., hardly differs from 



