366 THE POPULAR SCIENCE MONTHLY. 



I am further informed, to preserve the honor of the pupils ; but 

 to me it has always seemed like an object lesson in crime. 



Both by precept and example must justice be taught in our 

 schools, and its observance strictly enforced, before we may expect 

 to see fair play in the game of life. 



THE BAKOMETRIC MEASUREMENT OF HEIGHTS. 



By J. ELLAED GOEE. 



THERE are several methods of measuring the heights of moun- 

 tains and other elevated portions of the earth's surface above 

 the sea level. Of these maybe mentioned the following: (1) by 

 actual leveling with an engineer's spirit level and graduated 

 staff ; (2) by trigonometrical calculation based on the measure- 

 ment of the angles of elevation observed at the extremities of a 

 carefully measured base line ; (3) by observing the temperature 

 of the boiling point of water ; and (4) by reading a barometer at 

 the sea level, and again at the top of the mountain or elevation 

 the height of which is to be determined. 



The first of these methods is certainly the most accurate, but 

 it involves a considerable amount of labor, and for very high 

 mountains is sometimes impracticable. The second method is 

 sufficiently accurate if carefully carried out and a nearly level 

 plain is available for the measurement of a base line. The third 

 method is not accurate enough to give reliable results. The 

 fourth is the simplest and most expeditious of all. It is especially 

 useful for finding the difference of level between two points at 

 considerable distances apart, and would be sufficiently accurate if 

 certain difficulties could be successfully surmounted. A consider- 

 ation of this method and the difficulties to be overcome before its 

 accuracy can be relied upon may prove of interest to the general 

 reader. 



The principle of the barometric method is as follows: The 

 barometer measures the weight of the atmosphere. The column 

 of mercury in an ordinary mercurial barometer is equal in weight 

 to a column of air of the same diameter and of a height equal to 

 that of the earth's atmosphere. The densest portion of the atmos- 

 phere is that close to the earth's surface, and its density dimin- 

 ishes as we ascend. At the top of a mountain, therefore, the 

 pressure of the atmosphere will balance a shorter column of mer- 

 cury, and hence the mercury descends in the tube. From the 

 difference in height of the mercury at the level of the sea and on 

 the top of the mountain it is possible to calculate the height we 

 have ascended, as will be shown further on. 



