416 Account of an Hydraulic Orrery. 
.through it (when the syphon was charged) in a direction parallel 
to the vessel, which instantly began to move with accelerated ve- 
locity in an opposite course. Ina few seconds a maximum was 
attained, and the future progress exhibited that beautiful, conti- 
nuous movement which can only find an adequate comparison 
in the silent gliding of the heavenly spheres. The idea instan- 
taneously impressed me, and has been subsequently embodied 
with the most encouraging success in the novel machine above 
mentioned, ess VEE | | 
At present I have applied the principle, under appropriate 
modifications, no further than to the sun, the earth, and the 
moon, whose circuits, obliquities, parallelisms, and rotations, are 
displayed in apparently spontaneous. movements on an area of 
five feet diameter. To effect these, four floating syphons are 
so combinedin succession, that a quantity of water equal to the 
discharge of a single stream about 1-6th of an inch diameter, 
with a head of seven inches, elicits every action, Each motion, 
as in nature, is perfectly independent; any one may be checked 
without impeding another ; and when the hydraulic orrery com- 
mences its operations, it practically illustrates those incipient and 
gradually accelerating movements which may be supposed to 
have taken place within the mighty system itself, when, as in 
the beginning, the maximums of the greater motions were pro- 
bably attained in succession. 
This motive principle (founded on Barker’s mill, but now first 
combined with a syphon and applied to a floating body) is ap- 
plicable to an extensive variety of experimental and philosophical 
purposes. It is so truly equable, that I make the novel and inter- 
esting experiment of producing a perfect hydro-parabolic mirror 
54 inches diameter, and thus create any magnifying power ad /ili- 
tum. Whirling tables on this principle will preserve any particular 
velocity during any required period of time, and the motion ad- 
mits the most minute regulation, either by a variation in the 
length of the syphon, or of the size of the discharging aperture ; 
or by so fixing @ small flexible inclined plane to the syphon it- 
self, and bending it into the stream, as that any proportion of 
its reaction may be neutralized by its action. 
Another mean of obtaining an universal standard of measure 
_is hereby provided independently of the pendulum. Thus, a given 
parabolic speculum will invariably be formed by any given rota- 
tion at any known level and latitude, and the focal distance of 
any parabola must under those circumstances be always a given 
dimension. A graduated revolving circle will also practically 
measure such minute portions of time as are beyond the recog- 
nition of the most accurate astronomical clocks, My orrery, 
* when 
