into the switchboard sections is employed. At the Peak and
Kowloon Exchanges carbon filement lamps are used, On the
small Automatic Exchange at the North Point Electricity Works
a Calcium Chloride plant is employed.
268
(10). In modern practice in large exchanges in situations
where high humidities coincident with high temperatures are
experienced it is now usual to instal dehumidifying plants con-
sisting of refrigerating, washing, and heating units by means
of which all the air admitted to the switch and power rooms
is treated. A proportion of the moisture in the air is de-
posited by refrigeration. The air is then heated to a suit-
able degree and circulated to the rooms. A plant of this kind
has been provided at Penang in connection with a New C. B.
Manual Exchange installed recently. In Australia and in New
Zealand plants of somewhat similar character have been provided
at a number of Exchanges and excellent results are being ob-
tained from them. To protect the plant the relative humidity
in the exchange rooms should not exceed 70% at a temperature
of 70 to 75 degrees Fahr,
(11), From temperature and humidity records which Mr.
Claxton, the Director of the Royal Observatory, has been good
enough to furnish me with I find that during the summer months
temperatures ranging from 80 to 90 degrees Fahr, with relative
humidities of 80% to 95% prevail and for considerable periods
there is but little variation in the atmospheric conditions
throughout the 24 hours of each day. Under these conditions
and with the experience already gained on the existing Magneto
exchanges I consider it essential that dehumidifying plants of the type above described should be installed at the new Victoria and the Kowloon Exchanges referred to hereafter.
Comparison of Common Battery Manual and Automatic Systems.
(12). The C.B. Manual superceded the Magneto in large ex-