108 Mr. T. Hopkins's Observatiojis on Malaria. 



aflPected by their proximity to, or distance from, the conti- 

 nent." (See table of relative mortality at the end.) 



The atmosphere in which we live, it is well known, has 

 within it azotic gas, oxygen, a small portion of carbonic acid 

 gas, and invisible vapour of water, or steam. The nature of 

 the three first-named substances, as far as respects their in- 

 fluence on animal life and health, is tolerably well known ; 

 but the same cannot, I believe, be said of the steam which 

 exists in the atmosphere; nor am I aware that any scientific 

 attempt has been made to trace its influence on the animal 

 oeconomy with relation to health and disease. It is known 

 that too dry an atmosphere is productive of unpleasant 

 and sometimes of very painful consequences. Evaporation 

 from the body goes on so freely as to deprive it in too great 

 a degree of moisture and to produce a constant thirst. A 

 certain degree of moisture in the air keeps the body soft and 

 "ives that clearness of complexion common in many parts of 

 the north-west of Europe, which is supposed to indicate vi- 

 gorous health. Biit in odier parts of the world there is, 

 with reference to the animal oeconomy, a superabundance of 

 steam in the atmosphere. This is popularly recognised in 

 those parts when it takes the form of dampness, as it is then 

 thought to be injurious to health ; but it has not been treated 

 of scientifically. In the absence of any treatise on the sub- 

 ject I propose to call attention to a few points, in the hope 

 that it may induce others to institute a full inquiry, meteoro- 

 logical, chemical and physiological, such as the important 

 nature of the subject demands. 



Let us imagine that at some certain time no vapour exist- 

 ed in the atmosphere : according to the known laws of eva- 

 poration vapour would immediately begin to arise from all 

 wet surfaces ; and supposing evaporation to proceed, the whole 

 of the space occupied by the atmosphere would soon be filled 

 with vapour, or invisible steam ; the quantity being propor- 

 tioned to the temperature of each particular place. Where 

 the temperature was low there would be but little steam, 

 where it was high there would be more, and eveiy part would 

 in time have its maximum quantity, when of course no more 

 could rise. In this state, as there would be no condensation 

 of vapour, there would be no clouds and no rain. But owing 

 to the unequal influence of the sun on different parts of the 

 earth's surface, and the diurnal motion of the globe, this 

 state of things does not exist. Between the tropics the sun 

 vaporises water freely, and at the same time by its heat 

 rarefies the air. The vapour ascends with the rarefied air 

 to the upper regions of the atmosphere, cold air flows in below 



