140 
On Sensible Temperature . 
[May 1 
temperature, i. e. the number of degrees it falls in a unit of time. So that, used 
in this manner, the thermometer may really become an index to the feelings ; and 
they may, though in their own nature vague and fleeting, be not only measured, 
but fixed. Thus if in certain circumstances the thermometer lose 10° in a unit 
of time, we may be always sure that when the thermometer loses 10° in the same 
unit of time, the circumstances affecting the cooling process will be the same; 
and that, consequently, the accumulation or deficiency of beat in the human body 
will be the same ; in other words, that we shall feel equally warm or cold. And if 
we do not, we may infer that the usual action of the calefacient organs, whatever 
they be, is modified. Whether such modification may be the cause or effect of 
disease, or neither the one or the other, is one of the many questions which the 
full prosecution of the enquiry is calculated to throw light on. 
The case is, however, not even yet strictly parallel ; and this is owing to the ah* 
sence of the last of the conditions which regulates the cooling process — i. e. si- 
milar state of surface as to evaporation. There is, in fact, a difficulty in establish- 
ing this identity of state, and it is the chief difficulty with which the question is beset. 
The animal surface remains, if not absolutely dry, yet dry to sense at low tempe- 
pei'atures, while in higher temperatures the surface becomes covered with a dew, the 
evaporation of which must tend greatly to check the accumulation of heat. Indeed 
we have already seen that it is one of the means used by nature to keep the tempe- 
rature from ever exceeding a certain height. Now no inanimate substauce can 
be contrived so as to imitate the animal surface in this particular. And, therefore, 
we shall, I fear, fail to get an accurate answer to our question, — What is the sen- 
sible temperature of such a medium, under such and such circumstances ? 
Yet I would not he understood to despair altogether of an accurate solution to 
the problem of the sensible temperature. The fact is, that by adopting certain 
precautions we may obtain what appears very like a tolerable approximation. The 
naked thermometer raised to the temperature of the blood, and then allowed to 
cool, shows, by the rapidity or slowness of its fall, the tendency of animal heat 
to be dissipated or accumulated, as far as depends on the four first conditions of 
the cooling process. By covering it with cambric muslin, and keeping it moist, 
we may also have an idea of the proportional effect of evaporation, under certain 
circumstances, in modifying that effect. It is true that we cannot add this effect 
to the other, because we know not whether, under all circumstances of the case, 
(for instance at low temperatures,) the comparison or parallel will hold. Still, as 
our enquiries into sensible temperature are chiefly interesting with regard to the 
warmer countries, this contrivance will enable us to obtain some interesting 
comparative results. 
And it may be a question, whether what is called insensible perspiration may not 
be (at very low temperatures even) so copious as to allow of results being coin- 
paied at all temperatures. At least it will be interesting to ascertain at what de- 
gree of sensible temperature, i. e. under what accumulation of heat, this salutary 
process first manifests a cooling power. And it is evident that till we had a 
method of investigating and measuring the other circumstances which affect the 
cooling process, this could not be affected. 
A paper was read on this subject some years ago in England, before one of the 
medical Societies, by a Physician, who, sufficiently aware of the fallacy of the com* 
mon method of referring to the mere indication of the thermometer, failed yet to 
take a full and philosophical view of the subject. He proposed, in order to measure 
the sensible temperature, that a thermometer should be heated 10° above the tem- 
perature of the air, and the number of degrees being noted, which it would fall in 
one minute, when exposed to the cooling influence of the atmosphere, that number 
he considered would be an expression for the state of the air as capable of acting 
?. fee l in ? *• But ^dependent of his overlooking altogether the importance of 
ding to the state of the surface, as to moisture, and the effect of evaporation on 
(e S ideS 0 Sp'^ Un fl 0n “ erroneo " s «™eptio n of the laws of coiling. For 
onie hr ' g . ,nflue “ ce exerted on a b ° d y only 10* above the temperature 
a mea5ure of the cooling influence eserterl on the human 
bodv whifl» oi.„ .1 1 touting innuence exerted on tne huh***" 
or 6°’ZZtl TeteZ yS 16 'temperature, i e. 98-, and may consequently be 5* 
above it •— besides thifnr ° f ^ °- r any number from 10 ° to 100°, or even more 
tance It s ltt hi ^ ection > there is another of scarcely less imp*- 
alike as the simile AU? * ° f , bodies does not proceed, supposing other things 
tween tem P<»ature, but as some fractional power be- 
fell, that a bodv ZZZ r SqUHre * . The effect of this law is ’ for instanCe ’ 
) heated 10 above the air will not cool twice as rapid 1 / as 
