44 Mr. A. M. Worthington on 
capable of very exact measurement ; while the weight of liquid 
raised is that of a column whose height can indeed be accu- 
rately measured, but whose sectional area is again too small 
to be very correctly determined. | 
If a very wide tube be used, the perimeter can be measured 
with much greater accuracy ; but the weight of liquid raised 
cannot now be determined in the same way as before, since 
the volume included between the surface of the meniscus and 
a horizontal plane touching its lowest point is now an import- 
ant part of the whole volume raised. But the weight of the 
liquid raised along both the inside and outside perimeters 
of the tube is equal to the reactionary pull downwards of the 
liquid on the tube and may be determined by measuring 
this latter. 
M. Dupre’s wide cylinder of platinum foil was simply a 
tube whose inner and outer perimeters were sensibly equal 
and accurately known, and the pull across this perimeter 
could be determined in the way described. 
The great advantage of the coil over the single sheet is that 
the periphery across which the tension acts may be made 
very great, while the diameter of the coil, and consequently the 
quantity of liquid required and the area of its exposed surface, 
remains small. 
Thus one of my coils is made of a strip 50 centim. long 
and presents a perimeter of 1 metre, while its diameter is 
only 3 centim., and the pull of water on this is about 8 grams. 
The beads of which the strip is composed for separating 
the convolutions are made of hard glass, and strung on fine 
platinum wire, so that the instrument may be very readily 
cleaned by heating to a bright heat in the Bunsen flame. 
The beads should not reach within 2 or 3 centim. of the lower 
edge of the coil, in order that the liquid which rises between 
the convolutions may not reach so high as to wet the glass. 
If the consecutive coils are 2 millim. apart, then water (which 
is raised higher than any other known liquid) will attain a 
height of about °8 centim. But since the coil is liable to be 
dragged down into the liquid, it is well to leave an ample 
margin. 
If the coil dips below the plane surface of the liquid, there 
is a correction necessary on account of the buoyancy of the 
liquid. If, on the other hand, the base of the coil is raised 
above the free surface, there is a traction to correct for, due 
to the adhesion of the liquid to the horizontal section of the 
spiral edge. By adjusting the level of the liquid-surface 
after it has wetted the coil to the level of the base of the coil, 
when the balance-beam is horizontal, the necessity for these 
