MECHANICS, 
7 l 20 
the annular furface is the fame at q as at p, the fame quan¬ 
tity of fluid ought to be fupported in both tubes, whereas 
the tube E evidently raifes much lefs water than D. But, 
if we admit the fuppofition that the fluid is fupported by 
the whole furface of glafs in contaft with the water, the 
phenomenon receive^ a complete explanation ; for, (ince 
the furface of glafs in contaft with the fluid in the tube E 
is much lefs tlwn the furface in contact with it in the 
tube D, the quantity of fluid fuftained in the former ought 
to be much lefs than the quantity fupported in the latter. 
When a veil'd Fra, in the preceding figure, is plunged 
in water, and the lower part tuvzv filled by fuftion till 
the fluid enter the part of F t, the water will rife to the fame 
height as it does in the capillary tube G, whofe bore is 
equal to the bore of the part Ft. In this experiment the 
portions of water tvx and uxw on each fide of the co¬ 
lumn F x are fupported by the preflure of the atmofphere 
on the furface of the water in the velfel M N ; for, if this 
vefl'el be placed in the exhaufted receiver of an air pump, 
thefe portions of water will not be fuftained. Dr. jurin, 
indeed maintains that thefe portions will retain their po- 
fition in vacuo ; but in his time the exhaufting power of 
the air-pump was not fufficiently great to determine a point 
of fo great nicety. The column tux, which is not fuf¬ 
tained by atmospherical preflure, is kept in its pofltion 
by the attraction of the water immediately around and 
above it, and the column F tu is fupported by the attrac¬ 
tion of the glafs furface with which it is in contadr. Ac¬ 
cording to Dr. Jurin's hypothelis, the column t u x is fup¬ 
ported by the ring of glafs immediately above r, which is 
.a very unlikely fuppofition. 
The preceding experiment completely overturns the 
hypothefis of Dr. Hamilton, afterwards revived by Dr. 
Matthew Young. Thefe philofophers maintained, that 
the fluid was fuftained in the tube by the lower ring of 
glafs contiguous to the bottom of the tube ; that this ring 
raifes the portion of water immediately below it, and then 
other portions fucceflively till the portion of water thus 
raifed be in equilibrium with the attraction of the annu¬ 
lus in queftion. But, if the elevation of the fluid were 
produced in this way, the quantity fupported would be 
regulated by the form and magnitude of the orifice at the 
bottom of the tube ; whereas it is evident from every ex¬ 
periment, that the cylinder of fluid fuftained in capillary 
tubes has no reference whatever to the form of the lower 
annulus, but depends folely upon the diameter of the tube 
immediately above the elevated column of water. 
If the experiments which We have now explained be 
performed in the exhaufted receiver of an air-pump, the 
water will rife to the fame height as when they are per¬ 
formed in air. We may therefore conclude, that the af- 
cent of the water is not occafioned, as fome have ima¬ 
gined, by the preflure of the atmofphere afting more 
freely upon the furface of the water in the vefl'el than 
upon the column of fluid in the capillary tube. 
It appears from the following Table conttruCled by Mr. 
B. Martin, that different fluids rife to very different 
heights in capillary tubes ; and that fpirituous liquors 
■whofe fpecific gravity is lefs than that of water, are not 
raifed to the fame altitude. Mr. Martin’s experiments 
were made with a tube about i-^th of an inch in diame¬ 
ter. He found that, when capillary tubes charged with 
different fluids were fufpended in the fun for months to¬ 
gether, the enclofed fluid was not in the leaft degree di- 
tniniflied by evaporation. 
Names of the Fluids, 
Altitude. 
Conftant 
R umber. 
Common fpring water 
Inches 1 *2 
*048 
Spirit of urine 
- 11 
•044 
Tinfture of galls 
- i*i 
•044 
Recent urine - - 
- i’i 
•044 
Spirit of fait ... 
0*9 
•036 
Ol. tart, per deliq. 
- 09 
•036 
Vinegar - . 
- °'95 
•038 
Small beer - 
0*9 
•036 
Strong fpirit of nitre 
Altitude 
0*85 
Conftant 
Numbers. 
•°34 
Spirit of hartlhorn - - 
- 085 
*° 34 * 
Cream - 
o-8 
•03 z 
Skimmed milk 
- o*8 
•03 z 
Aquafortis - 
0*75 
•030 
Red wine ... 
- 0*75 
•03® 
White wine - 
0*75 
•030 
Ale - 
0 75 
•030 
O!. ful. per. campanam 
0*65 
•02 6 
Oil of vitriol - 
- 0*65 
•026 
Sweet oil - 
o*6 
•024. 
Oil of turpentine 
0*55 
*022 
Geneva - - - - 
o*ss 
•022 
Rum - 
0*5 
•020 
Brandy - 
o*s 
•020 
White hard varnilh 
P’S 
•020 
Spirit of wine 
0*45 
•018 
Tinflure of mars 
o* 4 S 
% oi8 
To the preceding Table, as given by Mr. Martin we 
have added the conftant number for each fluid, or the pro¬ 
duct of the altitude of the liquid, and the diameter of the 
tube. By this number therefore, we can find the altitude 
to which any of the preceding fluids will rife in a tube of 
a given bore, or the diameter of the bore when the alti¬ 
tude of the fluid is known ; for, flnee the conftant num- 
- C C 
ber C=DA, we (hall have D=—and A=— . Since the 
x\ JJ 
conftant number, however, as deduced from the experi¬ 
ments of Martin, may not be perfeflly correCf, it would 
be improper to derive from it the diameter of the capillary 
bore when great accuracy is neceffary. The following 
method, therefore, may be adopted as the molt correct that 
can be given. Put into the capillary tube a quantity of 
mercury, whofe weight in troy grains is W, and let the 
length L of the tube which it occupies be accurately af- 
certained ; then, if the mercury be pure, and at the tem¬ 
perature of 6o° of Fahrenheit, the diameter of the tube 
lw 
D=\ — X°'°i 9 H r > the fpecific gravity of mercury being 
13*580. The weight of a cubic inch of mercury being 3438 
grains, and the folid content of the mercurial column being 
D 2 LXo'7854, we (hall have 1 : 3438r=D 2 LXo*7854 : W. 
Hence, D 2 LXo'7854X 343 3 =;W ; and dividing we have, 
2— W _ I W “ 
~ L X_°' 7 8 54 X 3438’ ° f D— L = 0*7854 X 3438 a 
I W 
or D—\ —Xo'019241. If the whole tube be filled with 
mercury, and if W be the difference in troy grains be¬ 
tween its weight when empty and when filled with mer- 
'cury, the fame theorem will ferve for afeertaining the dia¬ 
meter of the tube. Should the temperature of the mer¬ 
cury happen to be 32 0 of Fahrenheit, its fpecific gravity 
will be 13*619, which will alter a very little the confiant 
multiplier 0*019241. 
When water is made topafs through a capillary tube of 
fuch a bore that the fluid is difeharged only by fucceflive 
drops; the tube, when electrified, will furnifti a conftant 
and accelerated Itream, and the acceleration is proportional 
to the fmallnefs of the bore. A fimilar effeft may be pro¬ 
duced by employing warm water, Mr. Lefiie found that 
a jet of warm water rofe to a much greater height than a 
jet of cold water, though the water in both cafes moved 
through the fame aperture, and was influenced by the fame 
preflure. A fiphon alfo which difeharged cold water only 
by drops, yielded warm water in an invariable Itream. 
Such are the leading phenomena of capillary tubes. The 
rife of fluids between two plates of glafs remains to be 
confidered ; and, while it furniflies us with a very beautiful 
experiment, it confirms the reafoning by which we have 
accounted for the elevation of fluids in cylindrical canals. 
Let ABEF and CDEF, fig. 28. be two pieces of plate- 
3 glafs 
