1811.] 
to what cannot be the cause of the heat 
in the land-winds. 
It remains now. to point out a theory 
supported on a firmer basis, which [ 
shall endeavour to do in the following 
pages. It is founded on a chemical 
penile, and will explain, I think, the 
eat of these winds ina satisfactory 
manner. ; 
The principle itself needs no demon- 
stration, as it is admitted as a general 
law; viz. that “all bodies, when they 
become more dense, suffer heat to _ 
escape; or, what is the same, they give 
out heat.” For example, when gases or 
aériform substances become vapours, 
they discharge as much heat as was ne- 
cessary to keep them in their former 
gaseous state: further, vapours in con- 
densing into fluids are known to do the 
same, as also fluids acquiring solidity. 
I am sorry that the quantity of heat 
set free in the condensation of vapours 
required for a pound of water, has escaped 
My memory; but I recollect it was very 
considerable. We know, however, that 
2 great deal of it is required for the eva- 
poration of the same measure, and it is 
» but reasonable to admit that the same 
quantity with which it has combined 
should be discharged on its returning to 
its former state of fluidity. 
In order to apply this principle to exe 
plain the presence of heat in our Jand- 
winds, I must first observe, that the at- 
mosphere in January, February, and 
March, is perfectly clear and serene; and 
then [ will call to mind what has been 
said of the phenomena of those winds, 
that they are preceded by clouds on and 
among the Ghauts, and that a heavy 
shower of rain from that quarter an- 
nounces their arrival; that during their 
continuance clouds are observed to lieon 
-the Ghauts; and that the atmosphere, 
even in the low country, is hazy and 
thick. I must add also, that the coun- 
tries west of the Ghauts are at this sea- 
_gon frequently visited by heavy showers 
of rain, accompanied with much thunder 
and lightning, and sometimes with hail, 
- Here in the Mysore country [ have found 
_the heaviest showers of this kind to come 
from the north-west,* which is exactly 
in the direction of the countries remark- 
able for the great heat of the land-winds 
Da Reh Aaa aS 1 Le or 
* The hottest land-winds in this season 
(1804) at Madras, were, I understand, from 
the north-west; which corresponds with the 
direction from which the rains came in My- 
§ore at that periods. | 
Medical Society. 
5 
in this season, At times, we have‘also 
showers from the east and south-east, 
and my attention shall not be wanting 
to ascertain whether it is not at the time 
when the land-winds blow hottest in the 
Carnatic. By this we see, that the 
clouds formed on the Ghauts, charged - 
with water and electricity (by causes I 
am not now to investigate), are drawn to 
the westward, whilst the heat, which du- 
ring the sermation of these clouds, must 
necessarily be discharged, is carried to 
the east or ta the lower parts of the coast, 
and causes the properties for which the 
Jand-winds are so remarkable. 
I have acknowledged already, that the 
heat occasioned by the power of the sun 
in this season, contributes to the aggre- 
gate of itin the wind; but [ must observe 
also, that it acts only as a secondary 
cause, and passively, by preventing its 
absorption and diminution in the career 
over a variety of substances, particularly 
moisture, with which it would combine, 
if they had not been previously removed 
or incapacitated, 
In colder climates, this absorption 
takes place in a greater degree, as sub- 
stances are abundant with which the heat 
produced by the formation of rain can 
combine and become iimperceptible.+ 
It is, however, there also often remarked, 
that the heat of the sun in a cloudy day 
is more powerful than at any other time. 
In common this is ascribed to the reflec- 
tion of the rays. of the sun from the 
clouds ; but I opine it is often the conse- 
quence of the formation of water in the 
clouds, which obscure the sky at that 
moment, d 
Tt has been observed, that the heat of 
the land-winds is not felt on the top of 
high hills, or on plains of a very inconsi- 
derable perpendicular height above those 
in which it rages most violently; as, for 
example, in Mysore near the Ghauts, 
which is only about five hundred feet 
higher than the valleys immediately be- 
low. This might be considered a weighty 
objection against my theory; as heat, 
considered in the light of an elastic fluid, 
expands equally on, all sides; and from 
whatever cause it proceeds, it should be 
supposed to extend even further where 
it meets with less resistance, as from the 
* Varl Dundonald’s Treatise, p. 20. ‘*The 
frequent changes in the degree of heat and 
cold in the atmosphere are to be ascribed more 
to the alternate disengagement and fixation 
of heat by chemical combination, than to the 
effects of the solar rays.” f 
air 
