302 ROCHESTER ACADEMV OF SCIENCE. [^lav 28. 



frost, rain, snow, hail ; (3) evaporation ; (4) cloudiness ; (5) wind ; 

 (6) barometric pressure, or the varying weight of the atmosphere. 

 The last has little direct or visible eftect upon climatic conditions, but 

 it has great indirect efi'ect by its control of the other elements. 



The many combinations of these elements in their varied intensity 

 produce the many kinds of climate and weather which give variety to 

 the physical conditions of the world. 



TYPES OF CLIMATE. 



The two main types of climate are the continental and the oceanic. 

 The continental type is characterized by extremes of temperature and 

 by great differences in the element of moisture and the distribution of 

 precipitation. The oceanic type has comparative uniformity ; small 

 differences between winter and summer, on account of the great ther- 

 mal capacity of water and its function of distributing and equalizing 

 temperature. A few figures in comparison of the two climatic types 

 will be interesting. 



Temperature. 



Average Maximum. Average Minimum. 



Equatorial Seas .... 90, and less 68 



Northern Continents ....113 -40 



Absolute maximum for Continent, 122 in Sahara and Death \'alley. 



" minimum " " -72 in N. A., -88 in Siberia. 



I\'Ionthly Averages of Teinperatiirc. 



Rochester lies so far inland that it might be expected to have a 

 mid-continental climate, with the usual extremes of temperature and 

 rainfall, but we find that it has an unusually moderate climate in all 



