Page:Journal of the American Society of Mechanical Engineers, Volume 33.pdf/669

charts as shown in Table 2 and Fig. 9. This shows that it is permissible ${\frac {1}{2800-1.2t'}}$ as the coefficient instead of ${\frac {1}{2803-1.329t'}}$, giving

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$e=e'-{\frac {(P-e)(t-t')}{2800-1.3t'}}$

Fig. 9.—Relation of Grains of Moisture from Government Tables to Grans Actually Contained.

Fig. 2.—Radiation Error in Wet Bulb of Sling Psychrometer.

This formula will give values of e for all wet and dry-bulb temperatures and all barometric pressures with an error of less than 0.5 per cent, assuming the chosen value of $C_{pa}$ to be correct.