584 MOSSOTTI ON A PHXZX NOMENON 
Neglecting in this equation the quantity — —_— —- — the 
i 
value of ¢ not being even given in this Huaptene as being 
too small and inappreciable, and substituting aA = 3°81, 
A = ‘908 A,, h, = 5:34 millimetres, and « = 1, we shall find 
T; =e 79 Ig A, 
which will be the expression for the force of tension of the sur-— 
face of the water in apparent contact with the oil; A, being the 
specific density of water taken as unity, and the linear unit being 
the millimetre. 
6. Having obtained this, let us now come to Dr. Young’s 
experiment. Into a small tube partly immersed in water, and | 
in which this fluid, by reason of capillarity, was raised almost to 
the upper extremity of the tube, he let fall a drop of oil, and saw 
the small column of water in the tube descend perceptibly. 
To calculate this experiment, I observe that the drop of oil on 
lying upon the water must also bend itself so that the concavity 
of its surfaces shall be turned upwards and terminate parallel to 
the sides. In this case therefore we shall have simultaneously 
w = 7, w, = 7, and consequently 
el | AT bs 
and the second equation (a.) will give 
Later leet at NC 
Be TY drain 
5 A a 
Let us neglect again the quantity = gas being small, 
1 
and substitute for T and T, their ante 3°81gA and ‘79gA,_ 
we Shall have 
i sks gE e = 8°50 millimetres, 
supposing the radius of tube to be one millimetre. 
Before letting the drop of oil fall upon the water in the tube of 
rad. = 1 millimetre, according to Gay-Lussac, the water ought to 
be at a height = 15°58 millimetres. After the oil has been placed 
upon it, ee to our calculation, it will not stand higher 
than 8°50. This ‘explains the perceptible depression observed 
by Dr. Young, which I proposed here to discuss. 
7. The difference between Poisson’s and my formulz arises 
