PLATINUM SURFACE AT HIGH TEMPERATURES. 
237 
In figs. 2 to 6 the full lines represent the formulae, the constants of which have 
just been given ; the points are the actual observations. The agreement between the 
calculated and observed results will be seen to be satisfactory. 
Tlie increase of emissivity with pressure in the case of air is sliown in fig. 7. 
Fig 7, 
On the Variation of Emissivity ivith Pressure. 
To return to the general formula for tlie heat dissipated. From the results so far 
obtained, we may write for pressures above 10 atmospheres 
Emissivity = ap"- -fi hjf [t,. — tg) = Vfp, t) + E 3 (i) + F 3 (^), 
