a new addition to the Slide-Rule. 



55 



graduation of the transverse bar. Referring to fig. 3, in 

 which MN is the width of the slide, and is the centre of 

 the radial arm stud-hole, for any index y, we have 



_MK_ MN + NO _MN , 

 7 "~ NJ ~ NO ~N0 +1 ' 



where OK is any position of the index line, or 



MN 



N0 = 



7 -l 

 Fig. 3. 



M 



*/ 



N 



3/ 









The following examples will serve as an illustration of the 

 class of calculation for which the instrument is designed. 



1. To determine the maximum pressure of an adiabatic 

 compression. 



Set the slide on back of cursor to 1*408 (<y). Suppose, for 

 example, that the initial pressure be 15 lbs. per square inch, 

 and that 100 vols, be compressed to 26 vols. 



Invert slide. Set index line of cursor to 15 on A, then set 

 1 (100) on g to index line of cursor. Now set index line to 

 26 on $j and read on scale A the corresponding pressure 

 = 100 lbs. absolute, 85 above atmosphere (figs. 1 and 2). 



2. The work done in any adiabatic compression can easily 

 be calculated from the above by the following formula : — 



w= 



7 -L 



PiVi 



where W = work done in ft.-lbs., V = final vol. of the gas 

 (after compression) in units of 12 cub. in. (to harmonize with 

 ft.-lbs. and pressure in pounds per square inch) , and p x = differ- 

 ence of pressure between adiabatic and isothermal maximum 

 pressure for the given ratio of compression (fig. 4). 



