HUMIDITY 
INSTRUMENTS AND METHODS 
It is difficult to discuss separately the instruments 
used for obtaining air temperatures and humidities on 
the Carnegie in that each of the four sets of thermal in- 
struments contained a wet- and a dry-bulb element. 
Therefore, since the mounting of the instruments has 
previously been discussed under the section on air tem- 
perature, only the wet-bulb equipment and methods will 
be elaborated on here. 
Assmann Aspiration Psychrometer 
Psychrometric observations were made daily atnoon 
(GMT) with an Assmann psychrometer, and the wet-bulb 
readings were used for correcting the wet-bulb records 
of the recording psychrometers. The wet-bulb tube of 
this instrument (P.T.R. No. 2450-1928) was a standard 
thermometer, and needed no corrections throughout the 
range of temperature encountered on the cruise. The 
usual precautions in using this instrument were observed. 
Negretti-Zambra Recording Psychrometer 
‘ The Negretti-Zambra capillary ventilating recording 
psychrometer was housed in the Stevenson screen on 
deck; the electric motor which operated the centrifugal 
ventilating fan was mounted outside the screen proper 
-and communicated with the psychrometer through a coil- 
spring coupling. The wick was moistened from a shal- 
low well immediately below the bulb, which was kept 
filled with distilled water from a reservoir connected to 
the well by a copper tube. The wicks were changed at 
frequent intervals. ea 
The Negretti-Zambra apparatus, especially the ven- 
tilating mechanism, required constant repairs. As the 
equipment was mounted athwartships, the rolling of the 
vessel produced strains on the coupling of the electric 
motor, which resulted in frequent breakdowns. In addi- 
tion, occasional failures of the electric current supply- 
ing power to the ventilating motor resulted in false read- 
ings. The observer was usually notified when this oc- 
curred, however, and appropriate notations and correc- 
tions were entered on the trace. 
No accurate check of the rate of ventilation was kept, 
but it was always sufficient to insure adequate ventilation 
of the wet-bulb except in the instances outlined above. 
It was frequently necessary to adjust the wet-bulb 
recording pen because of its tendency to fall slowly be- 
low the true values as determined by the Assmann psy- 
chrometer. Moreover, occasional spatial corrections 
were necessary owing to the fact that the psychrogram 
paper was noticeably affected by moisture and tended to 
buckle away from the drum during periods of rainor fog. 
Hartmann and Braun 
Electrical-Resistance Psychrometers 
Three pairs of Hartmann and Braun electrical-re- 
sistance recording psychrometers were mounted on the 
vessel at various heights above the deck (cf. fig. 2). The 
first was located in the Stevenson screen on deck (3.6 
meters above sea level), the second was housed ina 
Small naturally ventilated screen above the crosstrees 
39 
on the mainmast (21.9 meters above sea level), anda 
third was mounted in a similar shelter near the main 
truck (34.6 meters above sea level). 
These instruments were calibrated at frequent in- 
tervals against readings of the Assmann psychrometer; 
the one in the Stevenson screen was compared daily. 
The value of the recorded wet-bulb temperatures 
depends on the efficiency of the screens to a much great- 
er extent than is true in the case of dry-bulb readings. 
Obviously, the air movement through these naturally 
ventilated instrument shelters on the mast must fre- 
quently have been too slight to allow adequate ventilation 
of the wet-bulb. Therefore, it has not been possible to 
use the Hartmann and Braun traces to obtain continuous 
records of wet-bulb lapse rates. 
Evaluation of Psychrograms 
The corrections to the Negretti-Zambra and Hart- 
mann and Braun psychrographs were found by means of 
the noon readings of the Assmann psychrometer. These 
corrections were entered directly on the psychrograms 
and used to construct a corrected curve for obtaining 
the hourly values of wet-bulb temperature. The differ- 
ences between the hourly values of wet- and dry-bulb 
temperatures were later used for finding the vapor pres- 
sures and relative humidities according to the ““Aspira- 
tions-Psychrometer Tafelen”’ [Prussian Met. Inst., 
1930]. 
It is realized that the humidity observations are no 
more accurate than are the temperature readings them- 
selves. It is believed, however, that the errors in the 
cases of both wet- and dry-bulb readings should tend to 
cancel one another; for example, both will be affected in 
the same manner by overheating of the thermometers, 
etc., and the differences between the wet- and dry-bulb 
readings, therefore, should remain more or less con- 
stant. Thus, although the actual humidity measurements 
may be in error, the relation between humidity and air 
temperature should not vary greatly as the result of 
such errors. 
Wet-Bulb Lapse Rates Between 
Deck, Crosstrees, and Mainmast 
As explained, it has been impossible to obtain con- 
tinuous records of wet-bulb lapse rates between the 
Hartmann and Braun instruments at deck, crosstrees, 
and mainmast because of the possibility of errorsin air- 
temperature measurement resulting from overheating 
and undercooling of the thermometers. Reliable obser- 
vations are available in several cases, however, as are- 
sult of a calibration of the Hartmann and Braun instru- 
ments made with the Assmann psychrometer. The wet- 
bulb lapse rates recorded were usually normal, but 
three specific cases have been selected for discussion 
for the reason that they all were decidedly superadiabat- 
ic (see figure 15). 
1. July 29, 1928, at 12h, off the coast of Iceland: The 
wet-bulb lapse rate was 1:1 between deck and masthead 
or six times the saturated adiabatic rate. The weather 
was cloudy with a moderate northwest breeze. The sea 
was moderate with a surface temperature of 11°6. 
2. January 14, 1929, at 10h, entering the port of 
