CORRECTION FOR CAPILLARY ACTION. 



337 



The first shows the normal height of the meniscus when in contact with the air 

 (as is the case in the inferior branch of a siphon barometer), and in the barometric 

 vacuum at the top of the column, in tubes of different bores. It enables the observer 

 to judge better of its variations. 



Table XXIV. has been calculated by Delcros after the formulas of Schleiermacher, 

 making the constant x equal to 6 mm \5278, being the mean value between that of Gay- 

 Lussac = 6 mm .5262, and that of Schleiermacher = 6 mm '.5295. It gives the amount 

 of the capillary action in millimetres of mercury, taking into account both the size 

 of the bore, or the internal radius of the tube, which will be found in the vertical 

 argument, and the height of the meniscus, given in the horizontal argument. The 

 internal radius of the tube is supposed to be known ; the height of the meniscus, or 

 the vertical distance from the base, that is, from the sharp line where the mercury 

 ceases to be in contact with the walls of the tube, to the very top of the convexity, 

 can be ascertained by measuring it several times by means of the vernier. 



Example : Suppose the internal radius of the tube to be 3 mm -.2, and the height 

 of the meniscus to be O mm> .8 ; seek in the first vertical column the number 3 mm \2 ; 

 follow then the horizontal line as far as the vertical column headed O mm '.8, you find 

 there the number O mm> .776, which is the amount of the depression due to capillary 

 action, or the value of the correction to be added to the observation. 



Table XXV. is taken from Pouillet's Elements de Physique, Vol. II. p. 698 (1853). 



Table XXVI. is found in Gehler's Physicalisches Worterbuch, and in Schubarth, 

 Physicalische Tabellen, p. 21. 



Table XXVIL, which is Delcros's table reduced into English measures, gives the 

 means of correcting with more accuracy the indications of the English barometers. 

 For its use, see, above, the explanation to Table XXIV, 



Table XXVIII. is from Baily's Astronomical Tables. 



XXII. TABLE FOR THE CORRECTION TO 



.BE ADDED TO ENGLISH BAROMETERS 



FOR CAPILLARY ACTION. 



XXIII. TABLE OF THE HEIGHT OF THE 



MENISCUS OF THE BAROMETRICAL 



COLUMN. 



131 



