182 



of arbitrary degrees for a point at the 

 for all days in the years 1861-1870 : 



top of a house in that city 



These observations agree with those throughout the world in show- 

 ing that the intensity is least in the summer seasons and greatest 

 in the winter seasons of the respective hemispheres. There is also a 

 corresponding slight diurnal variation, in accordance with which 

 the intensity at a given point is least at 3 p. m. local mean time. 



