40 Influence of Atmospheric Pressure 



through intervening membranes, and in dependence on more 

 general physical laws), exposes in the same ratio their liability 

 to be altered or impeded by causes, which before scarcely came 

 into our view. 



The action of very dry air on the body is even less certainly 

 known to us. There is reason to believe that the effects of the 

 Simoom wind (exaggerated, perhaps, in common narrative) are 

 due in part to this cause ; — in conjunction with its singular 

 heat, the quantity of minute sand it conveys, and above all, the 

 electrical condition of the current air. There are more familiar 

 reasons, however, for presuming that the atmosphere may oc- 

 casionally be too dry (becoming so either naturally or by arti- 

 ficial means), for the healthy state of the functions of the skin 

 and respiration. Without referring to the question, still un- 

 decided, whether absorption of atmospheric moisture through 

 the surfaces of the body does occasionally or habitually take 

 place as a natural process, — and without affirming that the ef- 

 fect is derived from pulmonary evaporation unduly increased, — 

 we have various proofs that a state of air is often created by 

 artificial heat, insalutary to the body ; and that this condition 

 may be removed by means which restore to it a certain degree 

 of humidity. Houses or apartments heated by stoves (parti- 

 cularly under the style of domestic architecture in England), 

 are liable to suspicion on this score ; and if the fact be ascer- 

 tained, which is not difficult with the better hygrometers now 

 in use, it becomes expedient in every case to remedy it ; either 

 by exposure of a surface of water for the benefit of slow eva- 

 poration, or by other means. What is merely an inconveni- 

 ence for the hour or day, may pass into a serious injury to the 

 health, when there is long-continued exposure to it.* 



3. Pressure of the Atmosphere. — The influence of the atmo- 

 sphere in producing morbid conditions of body, through its 



* In a paper read before the Royal Society in 1836, on the ventilation of 

 the Custom-House of London, Dr Ure states the peculiarities of atmosphere 

 in the Long Room, warmed with hot air, and where 200 persons are always 

 present, to he its extreme dryness (sometimes 70 per cent, of DanielPs hy- 

 grometer), and negatively electrical state ; — the general effects produced being 

 vertigo, with a sense of fulness and tension about the head ; a quick but 

 feeble pulse ; and deficient circulation in the lower extremities. 



