312 J. LeConte—Horizontal Motions of small 
ted by even the best epee that the value of a for water 
in aclean glass tube is ze 
Moreover, even under ordinary conditions of temperature and 
pressure, the careful experiments of Quincket prove, that at 
the temperature of 20° (C.), the actual angle of contact (a) of 
water with clean glass in the presence of air =25° 32’. How- 
. ever, this factor being constant for any given temperature, its 
absolute value does not alter the result so far as the experimental 
test is concerned. For any given liquid at a given temperature 
if the postulate, that T or 'T’ is invariable, is true, we shou id 
have ALO aR ae Constant. Now, if A and h’, and 
4xXcosa@ 2Xcos a 
d and d’ are measured in centimeters, in the case of water w=1 
gram weight; so that the formule give the values of T and 
T’ in grams weight per centimeter of contour. Consequently, 
for water in contact with clean glass, we have 
-T per centimeter of contour = neeKS grams weight. 
, ud 
T’ per centimeter of contour = iat 
2cos a 
Now, gles to this fundamental postulate of the capillary 
grams weight. 
are not inconsistent wi the remarkable deductions Boscrssicet by the pet: 
p=molecular attraction ie the aioe for the liquid. Then, Clairaut in nese 
following laws: (1) When p=— the age is horizontal ; (2) When p> the 
meniscus is coneave ; (3) When p<t, the meniscus is convex. Now, in es case 
of water, alcohol, ether, ete., in seit with clean glass, at ordinary tempera Z 
tures, p> —: and assuming that when the temperature augments, the attraction 
‘of the solid for the liquid (p) diminishes faster than the attraction of the ta 
for itself (P); it is evident, that at a certain definite temperature, p must = — 
and bonseq yen, the meniscus becomes horizontal; and at a still higher tem 
perature pes, and the meniscus becomes convex. The experiments of Brimnet — 
and of Wolf have verified these deductions in the case of several liquids which ; 
wet glass. On the contrary, in the case of mercury in contact with glass, “ | 
so that, when the Yasser go augments p becomes still smaller, the m 
increases in ey and the depression is augmented. This last result cy 
been confirmed by the depo of Frankenhoin, who found the depress! 
mercury in glass tubes to be augmented se of te 
+ Phil. Mag., IV, vir xli, p. ba (Table X), pert In a later memoir Qut oe 
(Phil. Mag., V, vo ol. V, p. 325, 1878,) found this angle (a)=28° 48” for bast! , 
soi nea gee ig tubes. His $ experiments show that the value of a depen 
of the glass; but it never became zero, except under 5 Oat 
