REMEDIAL VALUE OF THE CLIMATE OF FLORIDA. 643 



ing a region on the east side of the State, from Jacksonville as far 

 south as Palatka. For a country lying on a parallel with the Canaries, 

 off the coast of Africa, they indicate a climate which in temperature 

 approaches that of Malaga, Malta, and Algiers, but does not nearly 

 equal them in evenness and unchangeableness, though, in point of 

 clear, sunshiny weather, far superior. 



However, from the facts given, we are unable to fix accurately the 

 position of the Florida climate. We neither know the atmospheric 

 humidity nor the electrical potential ; and, as yet, the phenomena of 

 nature have not been interrogated for an answer. 



A cardinal question is whether the climate be moist or dry, brac- 

 ing or relaxing. 



It may not be amiss to note here an error committed by a profes- 

 sional gentleman of Jacksonville.* In a pamphlet on the climatology 

 of Florida, he gives tables of the mean relative humidity of Jackson- 

 ville and other stations in Florida, and attempts to prove therefrom, 

 by comparison with similar observations in Northern States, that the 

 atmosphere of Florida is dry, much drier than that of Minnesota, Mount 

 Washington (New Hampshire), Alpina (Michigan), Omaha (Nebraska), 

 and other Northern localities. It should be remembered, however, that 

 there is a wide difference between relative humidity and absolute hu- 

 midity, and their relation is frequently diametrically opposite. Relative 

 humidity does not indicate the amount of vapor present in the air per 

 cubic foot, but only the tendency to deposit it in a wet state on a sur- 

 face but little lower in temperature than the surrounding atmosphere. 

 Absolute humidity, on the contrary, is the actual amount of vapor 

 present in each cubic foot of air. To illustrate, suppose the cubic foot 

 of air to be a hollow cubic vessel of tin. Absolute humidity is the 

 actual amount of watery vapor contained in that tin vessel. Relative 

 humidity is the tendency of that vapor, be it great or small in quan- 

 tity, to leak out of the vessel and show itself on the outside in the 

 form of mist or dew. Sir John Herschel says, " As a general meteor- 

 ological fact, there is not merely a want of accordance, but an actual 

 opposition between both the diurnal and annual progress of the ' de- 

 gree of humidity ' or ' relative humidity ' of the air and the ' tension 

 of vapor ' as indicated by hygrometric observation, a seeming para- 

 dox, but one very easily explained." f He then shows how the rela- 

 tive humidity is greatest just before sunrise of each day, and the 

 vapor tension or absolute humidity is least; that as the day advances 

 the relative humidity diminishes and the absolute humidity increases, 

 till the maximum temperature of the day is reached, when absolute 

 humidity is greatest and relative humidity is least. It is also well to 

 know, in considering this question, that air at a temperature of 60 

 Fahr. is capable of containing double the quantity of vapor by weight 



* Dr. J. C. Kenworthy. 



\ " Meteorology," by Sir John F. W. Herschel, Edinburgh, 1861, p. 193. 



