184 PHYSICS. 
which are so combined that all the even soldered joinings are on one side, 
and all they uneven on the other. The intervals between the single bars 
being filled by some insulating substance, the whole forms a compact 
bundle. That one of the two metals with which the pile ends is in 
conductive connexion with the point z, the other with y, so that these two 
points are to be considered as the poles of the battery. 
METEOROLOGY. 
PLatEs 23—29, AND PuatTeE 47 IN PART. 
Meteorology, an important and interesting branch of Physics in its more 
copious sense, on account of its extent is more usually treated of separately. 
This science has for its object the investigation and explanation of the 
physical phenomena which occur in the atmosphere, including all those 
known as meteors, not restricting the term to its more usual acceptation of 
shooting-stars. Meteoric phenomena may be distributed into various 
classes, including aerial (winds), watery (water spouts, &c.), optical, fiery, 
and electrical. The zodiacal light, and many of the _ shooting-stars 
which are sometimes embraced under the head of meteorology, in all 
probability do not belong here, as perhaps not falling within our 
atmosphere. 
A part of meteorology, and one not readily separated from it, is formed 
by climatology or the theory of climate, by this being meant the geogra- 
phical part of meteorology, or that which investigates the geographical 
distribution of those changes and phases of weather, constituting what is 
called the climate of a place. However great our interest in this subject 
of the weather and atmospheric phenomena in general, it cannot yet be 
denied that meteorology is behind al] the other departments of physics. 
This is caused by the great variety and complexity of most of the 
phenomena, but it is principally because we have not yet been able to 
collect a sufficient body of laborious, accurate, and long-continued 
observations from all parts of the earth to make our deductions. Much 
is due, however, to the labors and researches of A. Von Humboldt, 
Schouw, Dove, Schiibler, Kaemtz, Sabine, Reid, Piddington, Meyen, 
Redfield, Espy, Hare, and others. 
1. Chemical Constituents of the Atmosphere. 
The principal components of the atmospheric air are oxygen and 
nitrogen mixed nearly in the proportion of one to four. To speak more 
accurately, 100 parts of air contain twenty-one parts oxygen and seventy- 
nine nitrogen by volume, and twenty-three parts oxygen and seventy-seven 
parts nitrogen by weight. This ratio is to be considered as constant, and 
358 
