JuN'E 26, 1885.] 



♦ KNOWLEDGE ♦ 



639 



In reference to the wire, Rumford adds that it was not 

 included from any idea that such a metal could imbibe 

 moisture fioni the atmosphere, but in order to learn 

 ■whether it " is not cap;ible of receiving a small addition of 

 •weight from the moisture attracted by it and attached to 

 its surface." 



He further tells us that he was totally mistaken in his 

 conjectures relative to the other substances, lie says : — 

 " As linen is known to attract water with so much avidity : 

 and as, on the contrary, wool, hair, feathers, and other like 

 substances, are made wet with so much difliculty, I had 

 little doubt but that linen would be found to attract 

 moisture from the atmosphere with much greater force than 

 any of those substances ; and that under similar circum- 

 stances, it would be found to contain much more water. 

 And I was much confirmed in this opinion upon recollecting 

 the great diflerence in the apparent dampness of linen and 

 woollen clothes, when they are both exposed to the same 

 atmosphere. But these experiments have convinced me 

 thijt all my speculations were founded upon erroneous 

 principles." 



As already stated, the subject of the adhesion of gases 

 to solids was at that time but little understood ; the im- 

 portant fact that such adhesion eflfects great condensation 

 of the gases upon the surface of the solids was not under- 

 stood at all. It is this dense and firmly adhering film that 

 prevents the wetting by water in its liquid state. The 

 vapour of water being a gas, the paradox which puzzled 

 Rumford may be explained by this fact. His experiments 

 measured the quantities of gaseous water adhering to the 

 different fibres. 



This gaseous film being invisible and demanding careful 

 experimental research to demonstrate its existence, still 

 remains but little understood, and the crude idea that a 

 solid surface must be oiled in order to render it repellent to 

 water still remains rather obstinately fixed in the minds of 

 those who have not studied the subject. This is shown by 

 the letter of " G. A." No. 1,77G, page .533. A little 

 further study of the subject will teach him that thi.s " oil 

 gland," as he calls it (the uropygium), is by no means 

 peculiar to the duck or other aquatic bird.s. This has been 

 so long known that Paley, in his "Natural Theology," 

 dated 1802, describes it as a " sjiecific provision for the 

 winged creation " generally. The observations of Reaumur, 

 who found that these tail glands vary with the development 

 of the tail feathers, and are absent in those varieties of 

 fowls which have no tails point to their true function. If 

 " G. A. " will take the trouble to watch the action of a 

 duck or swan in preening its neck and breast, he will learn 

 that the old story of the bird squeezing out some tail oil 

 with its beak and then smearing it over its feathers is pure 

 fiction. I shall return to the subject of bird clothing when 

 I come to the uses of eider-down and the down of other 

 species of ducks, in human clothing. 



Rumford 8uggest< that the apparent dampness of linen 

 to the touch is analogous to the apparent heat of bodies 

 when similarly touched. Good conductoi-s appear much 

 hotter or colder than bad conductors of same temperature, 

 on account of the greater freedom with which the conduc- 

 tor parts with its heat when hotter than the hand, or takes 

 away the heat of the hand when cooler; so, he supposed, 

 may the linen more easily part with the small quantity of 

 water it contains. 



The fact is, that the linen is rml/i/ more wetable (to coin 

 a convenient word) than the flannel, as may be shown by 

 exposing an equal surface of linen and of flannel to the 

 same shower of rain and comparing the result. Much of 

 the water rolls off the woollen fabric, very little from the 

 linen before it has become taturated. 



Having by the above-described experiments shown that 

 the sheep's wool does ab.'^orb so much vapour of water, he 

 applied the results as follows, to explain the promotion of 

 insensible perspiration by wearing flannel next to the skin. 



" The persj)iration of the human body being absorbed by 

 a covering of flannel, it is immediately distributed through 

 the whole thickness of that substance, and liy that means 

 exjjosed by a very large surface, to be carried ofF by the 

 atmosphere ; and the loss of this watery vapour which the 

 flannel sustains on the one side, by evaporation, being 

 immediately restored from the other, in consequence of the 

 strong attraction between the flannel and this vapour, the 

 pores of the skin are disencumbered, and they are con- 

 tinually surrounded by a dry, warm, and salubriou3 

 atmo.sphere." 



There is one error in this description of the action which 

 modern research now enables us to correct. The loss sus- 

 taine.l by the flannel on one side is not due to rvapnralioit, 

 but to gaseous difl'usion. 



No two gases of different composition can remain in 

 contact with each other without mutually intermingling or 

 difl'using themselves through each other. This diffusion 

 is reducible to definite quantitative laws which have been 

 determined by the elegant and extensive researches of 

 Graham. But for this difTusion, and the fact that it over- 

 powers gravitation, we could not live upon the earth. 

 Every poisonous exhalation from decaying organic matter 

 or other sources would remain fatally concentrated ; the 

 heavy carbonic acid given off from our lungs and skin, 

 would flow down all the slopes of the earth, covering the 

 plains and filling the valleys with an invisible ocean of 

 sufTocating poison. As it is this gas, though bulk for bulk 

 nearly double as heavy as the other constituents of the 

 atmosphere, rises above the highest mountain tops, and 

 spreads freely and nearly equally throughout. The enormous 

 quantities generated in our crowded cities are always going 

 out of town, even during a dead calm. 



Aqueous vapour diffuses like other gases, and thus it is 

 removed from our bodies in the manner described in the 

 above quotation, if we merely substitute the word diffusion 

 for evaporation. This substitution is not merely a verbal 

 quibble, but expresses an important practical difference. A 

 closely-woven linen garment that is ri-eUed by the perspira- 

 tion does precisely what Eumford describes ; it absorbs 

 liquid water on the side next the skin, and this is evaporated 

 from the wet outside of the fabric, while the loosely-dis- 

 tributed fibres of a suitable woollen fabric take hold of the 

 vapour of the insfnsible perspiration in its gaseous form, 

 and by virtue of gaseous diffusion continually exchange 

 this with the gases of the outer atmosphere. Diffusion 

 must be taking place throughout all the gas-filled interstices 

 between the fibres, and the gaseous film adherent upon 

 the surface of each fibre must, by similar difl'usion, con- 

 tinually exchange itself with the surrounding atmospheric 

 gases. 



The significance of the figures in the above tabular 

 statement of Rumford's results will be better understood 

 by reflecting on the following. 



As the wool, ic, were weighed in the room where their 

 temperature was the same as that of the surrounding atmo- 

 sphere the adherent matter which added to their weight 

 was aqueous vapour, not liquid water condensed by cooling. 

 This theoretical conclusion is confirmed by the fact that 

 the ravelings of gold lace gained nothing — condensed no 

 water at all while exposed under the same conditions. The 

 specific gravity of aqueous water is lYaTi of that of water. 

 The specific gi-avity of wool fibre is a little greater than 

 that of water, about 1,800 times that of aqueous vapour. 

 Therefore the 1C3 parts of vapour gained by the sheeps' 



