XIX
311
ADIABATIC CHANGES IN MOIST AIR
temperature, so that the condensation of liquid water, i.e.
condensation above 0°, may just be avoided. To find the
answer we follow the line a as far as the isothermal 0° and
here meet with the dotted line 5.25. Thus we cannot have
more than 5.25 grammes of water per kilogramme of air.
To find at what temperature the air would then be saturated
at the pressure 750 mm., we follow the line 5.25 up to the
isobar 750 mm. and meet it at the temperature 4°.8. This
is the required highest value of the dew-point.
[The following editorial note occurs at the end of the number of
the Meteorologische Zeitschrift in which this paper appeared.]
We had already begun to print off this number when a letter from
Dr. Hertz arrived, a part of which we take the liberty of printing. At
the same time we are glad to have the opportunity of publishing in our
journal the introductory part of his paper. It is all the more valuable
because its results agree satisfactorily with those of Guldberg and Mohn,
while the method by which they are obtained is to a certain extent
different and follows more closely the papers of Clausius, etc. The
papers by Guldberg and Mohn, to which we have drawn the attention of
Dr. Hertz, are not easily accessible, and the subject is of so much im-
portance in meteorology that an exposition of it in another journal is by
no means out of place. Dr. Hertz writes us :—
My best thanks for the paper by Guldberg and Mohn
which you have so kindly sent me. Had I known of it
before I should have omitted the whole of part A of my
paper; for, as a matter of fact, except in notation, it corre-
sponds exactly with the calculation of Guldberg and Mohn.
Yet in investigating with the aid of my diagram the example
calculated by Guldberg and Mohn I became rather alarmed.
Down to 0° things went all right, but on proceeding further
I found that, according to my diagram, the mixture reached
the temperature -20° at 320 mm. pressure, whereas Guld-
berg and Mohn with their formulæ get 292.73 mm.
(6
An error of 28 mm. was too large, and I felt much afraid
that I had made some mistake in the construction. But it
appears that Guldberg and Mohn have made an error in
working out the numerical example, for I have repeatedly
made the calculation with their own formulæ and constants,
and always find 313 mm. for the pressure in question. Thus
there is at most a difference of 7 mm. between the exact