Weather Study 865 



Temperature of the Atmosphere 



The condition of the atmosphere with respect to its temperature is 

 determined by means of the thermometer. This instrument is in such 

 common use that a detailed description is not necessary. It might be 

 interesting to note that the instrument invented by Galileo was very 

 different from those now in use. Galileo's original thermometer was what 

 is known as an air thermometer, and its operation when subjected to differ- 

 ent degrees of heat or cold depended upon the expansion and contraction of 

 air instead of mercury or alcohol. It had one serious defect, viz. , the length 

 of a column of air is affected by pressure as well as by temperature and it 

 was, therefore, necessary, when using this thermometer, to obtain the pres- 

 sure of the atmosphere by means of the barometer before the temperature 

 could be determined. This is obviated in the modern thermometer by the 

 use of mercury or alcohol in a vacuum tube. Mercury is not used when it 

 is expected to register very low temperatures, because it congeals at about 

 45 degrees below zero Fahr. 



Thermometer Scales in Use 



There are three systems in common use for marking the degrees on the 

 scale, viz., Fahrenheit, Centigrade and Reaumur. 



The Fahrenheit scale was the invention of a German by that name, but it 

 is worthy of note that this scale is used principally by English speaking 

 nations and is not in common use in Germany. Fahrenheit found that by 

 mixing snow and salt he was able to obtain a very low temperature, and 

 believing that the temperature thus obtained was the lowest possible he 

 started his scale at that point, which he called zero. He then fixed the 

 freezing temperature of water 3 2 degrees above this zero, and the boiling 

 point of water at 212 degrees. There are, therefore, 180 divisions or de- 

 grees between the freezing and boiling point of water on the Fahrenheit 

 scale. 



The Centigrade scale starts with zero at the freezing point of water and 

 makes the boiling point 100. Thus 180 degrees on the Fahrenheit scale 

 equal i oo degrees on the Centigrade. The Fahrenheit degree is, therefore, 

 only a little more than half as large, to be exact five-ninths of a degree, as a 

 degree on the Centigrade scale. The Centigrade scale is in common use in 

 France and is used almost exclusively in all scientific work throughout the 

 world. 



The Reaumur scale is used generally in Russia and quite commonly in 

 some parts of Europe, especially in Germany. On this scale the zero is 

 placed at the freezing point of water and the boiling point at 80 degrees. 

 The divisions are, therefore, larger than those of the Centigrade scale and 

 more than twice as large as the Fahrenheit. The general use of these 

 different scales has led to endless confusion and made the comparison of 

 records difficult, so that even at the present time when making a tempera- 

 ture record it is necessary to indicate the scale in use. 



Distribution of the Temperature and Pressure 



The heat received on the earth from the sun is the controlling factor in 

 all weather conditions. If the earth were composed of all land or all water, 

 and the amount of heat received were everywhere the same throughout the 

 year, there would be no winds, no storms and probably no clouds and no 



