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LXIV, On Capillm-y Attraction. By the Rev. J. B. Ewmett,* 



[Continued from p. 118.] 

 T^HE force which elevates a column of liquid in a fine 

 -^ tube, between two plain surfaces, or around solid mat- 

 ter generally, is corpuscular : the effect is produced by either 

 the surface only of the solid, or a stratum of immeasurably 

 small depth. The liquid is elevated by the attraction of 

 the solid to its upper strata : for, if the upper strata alone 

 of the suspended column be heated, as great an effect is pro- 

 duced as by heating the whole column to the same tempera- 

 ture, which is apparent when the mechanical principles upon 

 which the phaenomenon depends are considered. 



This fact I did not ascertain until very recently : I had 

 gone through a long series of experiments, using a test tube 

 which contains the liquid, into which is inserted the capillary 

 tube, along which an index moveable by a fine screw, having 

 a divided head, slides : the liquid having arrived at its proper 

 altitude, the whole was plunged into water or other liquid 

 heated to a given temperature, the index being a little above 

 the surface. After having repeated a great number of experi- 

 ments, many of which were anomalous, I found those which 

 had occupied several weeks wholly useless. The whole series 

 must be repeated by help of an apparatus, which will allow the 

 suir.mit of the column to be seen, and by which any required 

 temperature may be applied to the upper part only. These 

 experiments being useless, I was not able to communicate a 

 paper for the last Number. 



In the former paper, I showed that if the density of a liquid 

 be changed by expansion or contraction, the altitude of the 

 column is not affected. This may be proved experimentally: — 

 Heat as much as possible of the capillary column, except the 

 upper sti-ata, and no sensible effect is produced : apply the 

 same temperature to the upper part, and a notable depression 

 takes place, such as 3 or 4< parts in 20 ; even the heat of the 

 hand causes a depression of about j\jth of an inch in a column 

 of 2y^jj inches. 



I now proceed to investigate the phaenomena of such com- 

 pounds as saline solutions, dilute acids, &c. Let thei'e be two 

 substances, A and B ; let the compound be C. 



Let a = sp. gr. A h = sp. gr. B c = sp. gr. C 



d = weight of A e = weight B y = weight C = d + e 



H = altitude to which A is elevated; h = altitude B; 

 /i' = altitude of C. 



* Communicaled by the Author. 



The 



