Peo «| 
Ill. A Capillary Multiplier. 
By A. M. Worrturineton, M.A.* 
[Plate I. figs. 1 & 2.] 
: veer little instrument (Plate I. fig. 1) consists simply of a 
rectangular strip of platinum foil of known length rolled 
into a cylindrical coil, whose successive convolutions are kept 
separate at a distance of about 2 mm. by means of a strip of 
glass beads in the upper portion of the coil. The lower 
edges of all the convolutions are in the same plane ; and the 
instrument when in use hangs from one end of a balance- 
beam with this plane horizontal. 
The liquid whose surface-tension is to be determined is 
placed below the coil in a vessel which can be raised till 
the free surface touches the base of the coil. The pull now 
exerted on the coil is measured by weights placed in the 
other pan ; and these weights afford, when certain precautions 
shortly to be mentioned are taken, an accurate measure of the 
surface-tension of the liquid. 
The method is really that used twenty years ago by Wil- 
helmyt, and more recently by M. Duprét, who, however, 
employed only a single cylindrical sheet of platinum instead 
ofa coil, and an hydrometer instead ofa balance for measuring 
the pull. 
The only novelty lies in the substitution of the coil for 
the single sheet, by which the sensitiveness of the method is 
increased many-fold. 
The principles involved may be briefly explained as follows : 
When any liquid is placed in a vessel whose sides it wets, 2. e. 
against which the edge-angle of the liquid is 0°, the liquid is 
raised round the edge above the level of the free surface, 
and the weight of liquid so raised is equal to the surface- 
tension of the liquid multiplied by the periphery across which 
the surface-tension acts. When the periphery (p) is known 
and the weight (wv) of liquid raised is known, then the tension 
per unit of length is known to be =, 
When a capillary tube is used for measuring the surface- 
tension, the periphery across which the force acts is the 
internal perimeter of the tube, and this is too small to be 
* Communicated by the Physical Society: read November 22, 1884 
(communicated by J. H. Poynting). 
Tt Poggendortf’s Annalen, 1863, No. 6, p. 177. 
t See Théorie mécanique de la Chaleur, par M. A. Dupré (Paris, 1869), 
p. 245 et seq. 
