NATURAL PHILOSOPHY. 175 



OX THE MOVEMENTS OF FLUIDS IN POROUS BODIES. 



Among the topics of scientific interest which awaken attention at present, 

 is the research of Jamin, professor at the Ecole Poly technique, upon the 

 equilibrium and movement of fluids in porous bodies. The new results at 

 which he has arrived afford an explanation of the ascent of the sap in vege- 

 tables without the necessity of recourse to the vital force. It is apparently 

 a question of capillarity only. 



Jamin has applied the new facts which he has discovered to the construc- 

 tion of an apparatus composed entirely of inorganic materials, but showing 

 in its structure a great analogy with vegetables. This apparatus has the 

 property of raising water, as trees do, to a height greater than that attained 

 by means of atmospheric pressure, from a moist soil, whence the water is 

 constantly drawn to the factitious leaves, where it is continually evaporated. 



Reduced to its most simple form, this apparatus is composed of a block of 

 some well-dried porous substance, as chalk, lithographic stone, etc., or a 

 porous battery cell filled with a powder well rammed in, white chalk for 

 instance, oxide of- zinc, or even with earth. A manometer is imbedded in 

 the interior of the mass, and the whole is plunged in a vessel full of water. 

 The water immediately penetrates its pores and drives out the air, which, 

 collecting in the interior, exercises a pressure upon the manometer amount- 

 ing with oxide of zinc to five atmospheres, and with starch it exceeds six 

 atmospheres. This is not the limit of the greatest possible pressure; Jamin 

 makes known the causes which diminish it in these cases, and proves that 

 the water is forced into porous bodies with a force which he calls TT, and 

 which is equal to that of a considerable number of atmospheres. A tube 

 1.20 metres long, filled with plaster and terminated at the summit by an 

 evaporating surface, is inserted by its base into a reservoir closed and filled 

 with water; a vacuum is caused, mcasm-ed by fifteen or twenty millimetres 

 of mercury, or by two hundred or two hundred and seventy millimetres of 

 water; and the water appears even at the upper extremity of the tube 

 which proves porous bodies are able to raise water higher than can be done 

 by atmospheric pressure. These facts cannot be explained by the ordinary 

 laws of capillary attraction, since these bodies are not formed of impermea- 

 ble tubes, but of corpuscles in juxtaposition, separated by small empty 

 spaces. Jamin has therefore submitted the problem to the calculus, and has 

 come to results, of which we mention the following: 



If, in a damp porous body, the water is compressed by a power of several 

 atmospheres, it can congeal only at a temperature below C. 1 Consequently 

 old wood is able to resist frost, while young shoots, being less dense, are 

 unable to do so. 



Since water, in filtering through a porous body, is compressed as it enters, 

 and dilates again as it runs out, it should exhibit electric currents and many 

 other phenomena. 



The theory cannot be applied to non-homogeneous porous bodies. In the 

 extended memoir which he has prepared, Jamin discusses the complicated 

 results which may be occasioned by irregularity of structure; he makes an 

 application of it to wood, and shows that the interior pressure must be aug- 



1 This fact has just been demonstrated by Mr. Sorby for water contained in capil- 

 lary tubes of a small diameter. 



