METEOROLOGICAL EQUIPMENT FOR SHORT WAVE 229 
It is well known that the ordinary thermocouple is 
not readily adapted to recording purposes. Only at sta- 
tionary installations such as towers, where multi- 
junction thermopiles can be used, is it possible to 
record the indication of the sensitive galvanometer 
required. 
Anemometers 
Wind measurements are of importance in connec- 
tion with off-shore winds at coasts which give rise to 
pronounced refraction of short and microwaves. The 
ordinary commercial anemometers become quite un- 
reliable at very low wind speeds (of the order of 4% m 
per second) and may stop completely. A special ane- 
mometer for low wind speeds® has been designed by 
the British Chemical Warfare Service and is used as 
a regular piece of field equipment by its units. In the 
United States a highly sensitive anemometer has been 
developed at the California Institute of Technology.” 
This instrument records wind speeds from 0.5 to per- 
haps 30 mph. It has the conventional three cups rotat- 
ing on a vertical axis. Hach rotation is registered on a 
counter by magnetically operated electrical contacts. 
For higher wind velocities the counter may be switched 
to record only every hundred rotations. The apparatus 
is delicate and is critical in its behavior toward certain 
adjustments. 
Semipermanent Installations 
TOWERS 
Two major installations of towers are at present in 
existence in England. They are the Porton towers and 
the Rye towers. The Porton towers on the Salisbury 
Plain form part of the extensive meteorological equip- 
ment of the British Chemical Warfare Service and 
have been in use for a considerable number of years.® 
Continuous records of dry and wet bulb temperatures 
at heights of 4, 23, and 56 ft above the ground are 
made. The elements used are platinum resistance 
thermometers connected into bridge circuits and are 
artificially aerated. The recording mechanism is lo- 
cated near the bottom of the tower. 
A similar set has recently been installed on the Rye 
towers in Sussex which form part of a CH radar sys- 
tem. Temperature and relative humidity are recorded 
for heights of 4, 50, 155, and 360 ft above ground. The 
resistance thermometers are similar to those at Porton, 
but the moisture measurements are made with the 
Gregory humidiometer described above. 
In a large research project on microwave refraction 
carried on in the summer of 1944 by the Propagation 
Group at the Radiation Laboratory, a mast was erected 
at one terminal of the path. Wet and dry bulb tempera- 
tures are recorded continuously with the device de- 
scribed in text on p.228 at heights of 4, 16, 36, and 
55 ft above the sea surface, these heights varying some- 
what with the tide. The measuring elements are lo- 
cated in one end of a horizontal piece of tubing 3 ft 
long, and in the other end, close to the pole, an aera- 
tion fan is mounted. Wind yelocity records are made 
by means of Stewart anemometers. 
SHIPS 
The Royal Navy has detailed three yachts for atmos- 
pherie measurements on an experimental microwave 
transniission path over the Irish Sea. They are pro- 
vided with dry and wet thermocouples at altitudes of 
5, 10, 40, and 50 ft above sea level. The former two 
are mounted on hinged beams outboard, while the 
latter two are on a mast in the forward part of the 
ship. The thermocouples are copper-constantan, and 
there are two in series for the temperature measure- 
ment with the cold junctions placed in a Dewar flask 
filled with melting paraldehyde (maintaining a tem- 
perature of 50 F). There are two pairs of dry and wet 
Junctions connected in series which measure the wet 
bulb depression. The galvanometer is in the ship’s 
cabin. Aeration is provided by the ship’s movement, 
and when measurements are made the ship sails into 
the wind to minimize the effects of the discharge from 
the smokestack. 
In the project at the Radiation Laboratory just re- 
ferred to measurements are also being made from the 
mast of a boat. The 48-ft mast is provided with a 6-ft 
cross arm and a motor-aerated housing containing the 
elements can be raised from the bottom of the mast 
to the end of the cross arm, giving continuous infor- 
mation over the height of its travel. 
Measurements carried out on shipboard by means 
of captive balloons or kites will be discussed in fol- 
lowing text. 
Measurements on Board Planes 
and Dirigibles 
As has been mentioned before, a sling psychrometer 
held out of the window of a flying plane will give 
reasonably accurate results if some elementary pre- 
cautions are taken to insure proper moistening of the 
wick. 
The two types of instruments described before on 
p-228have been adapted for use with airplanes. In the 
Radiation Laboratory instruments the two elements are 
mounted diagonally in a piece of Bakelite tubing about 
14% in. in diameter, the dry element in front of the 
wet element, relative to the wind stream. In the earlier 
airplane measurements water was blown over the moist 
element and a reading made when the recorder showed 
equilibrium to be reached. Now capillary action is used 
throughout, the water being supplied from a small 
vessel underneath the Bakelite tube. This instrument 
has been tested in a wind tunnel with wind speeds up 
to 145 mph. The dynamic pressure effect increases 
the reading by 0.4 C at the cruising speed of the plane 
(100 mph). This value was checked, both in the plane 
itself and in a wind tunnel. 
