THE HYDROSTATIC PROBLEM FOR THE ATMOSPHERE. 79 



some special auxiliary lines and auxiliary divisions. These are also shown on figs. 



8 and 9 belonging to the examples. When extended work of this kind is to 

 be performed, the best method of saving time will therefore be to print such 

 special blanks. 



When the observations of pressure are recorded in millimeters of mercury and 

 those of temperature in centigrade degrees, the blanks should contain (see fig. 8) : 

 (1) horizontal lines representing the standard isobaric surfaces ; (2) virtual-temper- 

 ature divisions on each of these lines. These divisions are obtained by using 

 table L, page 76, as explained in the preceding section. If these blanks be used 

 the somewhat time-wasting work of drawing by hand the lines representing the 

 standard isobaric surfaces drops out. Further, the virtual-temperature divisions 

 allowed us to draw the virtual-temperature diagram without using table 11 A'of the 

 Appendix. It is thus seen that in using these special blanks, the height of the 

 standard isobaric surfaces can be determined with practically the same ease as if 

 the observations of pressure had been taken in rational units. Some supplemen- 

 tary results, as for instance the specific volume of the air at the standard isobaric 

 surfaces, are also obtained with the same ease. But if the working out of the 

 example should be carried still further, if it be required, for instance, to determine 

 pressure in given heights, or to find the heights at which the observations were 

 taken, it will be the best plan to change from the beginning the observed pressures 

 from millimeters of mercury to millibars, and to proceed as in example 1. 



When the observations of pressure are given in inches of mercury, and those 

 of temperature simultaneously in Fahrenheit degrees, the blanks should contain 

 (see fig. 9): (1) special divisions along the axis of abscissas representing the centi- 

 grade degrees, while the main divisions are used to represent the Fahrenheit 

 degrees; (2) horizontal lines representing the standard isobaric surfaces ; (3) virtual- 

 temperature divisions on each of these lines. These divisions are found by using 

 table L, p. 76, in connection with the centigrade divisions along the axis of abscissae. 

 If these blanks be used, the following facilitations are obtained: The special draw- 

 ing by hand of each line representing a standard isobaric surface is no more required. 

 The virtual-temperature divisions allow us to draw the virtual-temperature diagram 

 without being obliged to refer to table 12 a of the Appendix. The use of table 



9 A of the Appendix for the transition from Fahrenheit to centigrade degrees is no 

 more required. In this way column 6a, table O, drops out, the centigrade tempera- 

 ture recorded in column 6b being found directly from the diagram. It is seen 

 that in this way, by the use of these special blanks, the height of the standard iso- 

 baric surfaces are found with practically the same ease as if the observations ot 

 pressure had been recorded in m-bars and those of temperature in centigrade 

 degrees. As in the preceding case, some supplementary results are also easily 

 obtained, such as the specific volume of the air at the standard isobaric surfaces. 

 Even these supplementary calculations are simplified by the centigrade divisions 

 along the axis of abscissce, column 90, of table O, dropping out when these divisions 

 are at hand. But if the example should be worked out still more in detail, if it be 

 required to determine pressure in given heights, or to find the heights at which the 



