746 
M E C H A N I C S. 
in the pump. In this cafe we evidently have 
■ = li 
from which we find t— sra —,=*78336 
Vgl y/i 
of a revolution in feconds, when no work is done. 
If the machine be effectual, the velocity of the dream 
can never exceed the velocity which a heavy body would 
acquire in falling down the difference between 33 feet and 
the height of the vertical leg; for a greater velocity than 
that would caufe a vacuity in the machine which would 
not be fupplied by the preffure of the atmofphere. Now, 
by the laws of falling bodies, the velocity acquired in fall¬ 
ing through the height 33— i is y/ 2^(33—/), and, by what 
/ / lit 2 ® 2 
is done above, the velocity of efflux is .y ^ 
gi 2 
, for the time 
Making thefe values equal, we have 
S l ~ 
■l— 33 - 
- 1 . 
From which we deduce t—na 
a a 
-— ’78336———• 13636a. 
31 g V 33 
If /= 33, then will the laft value of t be the fame as the 
preceding, and no difcharge can take place; agreeably to 
the obfervations at the beginning of this article. In all 
other cafes, having found the time of revolution when the 
water is ftationary, we have only to diminifh that time in 
the ratio of ^33 to y/l, and we fhall have the time of 
revolution when the work done is the greateft this pump 
■will admit of. 
The Hejjian pump is of the centrifugal kind. ABODE, 
fig. 55, are two tin veffels, foldered together, but commu¬ 
nicating with each other by a hole at the bottom. The . 
larger veflel is furniflied with a rim, to receive the water 
thrown up by the circulating tubes, and convey it into 
the vtffcl D E. m, n,o, p, fig. 56, reprefent four tubes of 
metal or glafs, open at both ends, but bent at top, and 
fixed in an angular pofition to the axis IK. When in 
their place, the extremity I of the axis refts upon a point 
at the bottom of the large veflel, while the upper part is 
Iteadied, and kept in a vertical pofition, by palling through 
a hole in a bar going over the large veflel at A B. To 
/how the operation of this pump, fill the veffels about two 
thirds with water, and then make the tubes circulate ra¬ 
pidly by turning the handle S; and the rotatory centrifui. 
gal motion will raife the water, and difcharge it into the 
imall veflel D E, by the pipe k. 
Analogous to the rife of water in pumps is its rife and 
motion in Jiphons. The fiphon is an inftrutnent ufed to 
decant fluids, or convey them from one place, over an ob- 
ftacle that is higher than their furface, to another that is 
lower. Its form is extremely Ample, being nothing more 
than a crooked tube, one extremity of which deicends 
lower than the other. Its effedfs are accounted for from 
the gravitation of fluids of different weights (water and 
air) one upon another. 
If one end of a fiphon mno, fig. 57, be put into a veflel 
of water, and the other end without be lower than the 
furface of the water; then, if the air be drawn out, the 
water will begin and continue to run, until the furface of 
the water in the veflel is on a level with the end 0. For, 
when the air is drawn out of the fiphon, the water will 
riie in it to n by the preffure of the air upon the furface 
of the water in the veflel, and then it will defcend to 0 
by its gravity. Now the preffure of the air at 0 to force 
the water in the direction on m, is equal to the preffure of 
the air on the furface of the fluid in the veffe! to force the 
water in the direction mno, at lealt, extremely nearly lo, 
on account of the very frnall difference of the altitudes of 
the air above m and 0 ; but the former preffure is oppofed by 
the preffure of the column no, and the latter p re flu re is op- 
poled by the preffure of the column m n ; the latter preffure 
of the air therefore being lefs oppofed than the former pref¬ 
fure, the fluid mult move in the direction of the latter 
preffure, or in the direction mno ; and the fluid will con¬ 
tinue to run til! the preffures of on,mn, become equal, or 
till 0 are in the fame horizontal line; for then, their 
perpendicular heights being equal, their preffures will he 
equal. Thus it appears that faction is owing to the.pref- 
fure of the air. 
The fiphon is an inftrument of extenfive and daily ufe. 
The ditlillers’ fiphon (fig. 58.) is ufifally about an inch in 
diameter, and three feet in length, with a cock fixed into 
the iffning end. To ufe it, the cock is ffiut, and the con¬ 
trary'end is put into the bung-hole, til! the liquor reach 
within about five or fix inches of the bend. Then, on 
opening the cock pretty, quickly, the contents flow out 
of the fiphon in the ufua! manner. By the immerfian of 
the drawing leg, the liquor is prevented by the pent-up 
air from riling as high within the fiphon as it is on the ont- 
fide. On opening the cock, the ambient fluid obtains 
power to raiie that within the tube to its own level ; but, 
by a law already explained, the contained liquor, before 
it rifes as high as that of the other, will have acquired a 
velocity nearly fufficient to carry it as much above that 
furface as it was before below it. Hence the fluid /hoots 
over the bend ; and there falling into a tube with a ccn- 
trafted orifice, the fyphon is loon filled, and of courfe 
continues to flow. 
Several entertaining deceptions have been pradfifed by- 
means of the fiphon. One of the molt ufuui is that of 
Tantalus's cup, a view of which we have given at fig. 59. 
where A B C D is a metallic veflel, divided into two parts 
by a partition F f ; in the middle of this partition is a 
ft nail round hole, to receive the tube MS, about two lines 
in diameter, the lower orifice of which mult defcend a 
little below the partition. This tube is covered by an¬ 
other fomewhat larger, clofed at the top, and having on 
one fide, at the bottom, an aperture, fo that, when water 
is poured into the veflel, it may force itfelf between the 
two tubes, and rife to the upper orifice S of the firit. This 
mechanifm nuift be concealed by a Imall figure in the at¬ 
titude of a man Hooping to drink, and having his lips a 
little above the orifice S. If water be poured into this 
veflel, as foon as it reaches the lips of the figure, being 
above the orifice S, it will begin to run off; and a fort of 
iiphonic motion will take place, in confequence of which 
the whole of the water will run into the lower cavity^ 
which ought to have in the fide, towards the partition, an 
aperture to let the air efcape at the lame time. This ma¬ 
chine might be rendered Hill more agreeable, by conftruft- 
ing the final! figure in fuch a manner, that, when the wa¬ 
ter has attained to ics utmolt height, it (hall caufe the 
figure to move its head, in order to approach it; which 
would reprefent the geflures of Tantalus, endeavouring 
to catch the water to quench his thirft. 
Upon the fame principle we may conflrudt a veflel which 
while Handing upright retains the liquor it contains; but 
which if inclined, as for the purpofe of drinking, imme¬ 
diately luffers it to efcape. Pierce a hole in the bottom 
or fide of the veflel to which you are delirous of giving 
this property, and infert in it the longer branch of a 
fiphon, the other extremity of which mult reach nearly to 
the bottom, as /sen fig. 60. Then fill the veflel with any 
liquor as far as the lower fide of the bent part of the 
fiphon ; it is evident that, when inclined, and applied to 
the mouth, this movement will caufe the furface of the 
water to rife above the bending, and from the nature of 
the fiphon the liquor will then begin to flow off; and, if 
the veflel is not reltored to its former pofition, will con¬ 
tinue doing lo till it becomes empty. 
This artifice might be concealed by means of a double 
cup, as it appears in fig. 61. for the fiphon abc, placed 
between the two fides, will produce the fame effeft. If 
the veflel be properly prefented to the perfon whom you 
are defirous of deceiving, that is to fay, in. fucli a manner 
as to make him apply his lips to the fide b, the fumniii 
of the fiphon, the inclination of the liquor will caule it to 
rife above that fununit, and it will immediately efcape at 
c. Tliole perfons however who are acquainted with the 
. artifice 
