Intelligence and Miscellaneous Articles. 31 1 



The annual motion of the planets round the Sun is caused by 

 the property which catgut strings have of twisting and untwisting 

 according to the state of the atmosphere. When the apparatus is 

 removed from a damp room into one which is drier, and hung up, 

 the catgut A twists and carries the rods B, C, D round from right 

 to left, thus showing the course in which the planets really move 

 round the Sun. 



The small bar E hanging by a string of catgut about three feet 

 long, makes several revolutions, whilst it is carried round the Sun 

 once; the Earth and Moon are connected with this bar at unequal 

 distances from the point of suspension, and are carried round this 

 point (which represents the common centre of gravity between 

 those bodies), the Moon by revolving round the Earth illustrating 

 the monthly motion. Owing to the relative lengths of catgut be- 

 tween the point of suspension of the string A, and the bars B, C, 

 and D, the difference in the annual motions of the planets is oc- 

 casioned. In the Planetarium here figured, the diameter of the 

 Earth's orbit is about one foot eight inches ; that of the Moon's 

 round the centre of gravity, between four and five inches. I have 

 one, of the Sun, Earth, and Moon, in which the diameter of the 

 orbit of the Earth is about six feet, and of the Moon about one 

 foot eight inches. 



On the principle of this machine, the rest of the Solar system 

 usual on Orreries may be added ; and where a considerable length of 

 catgut can be conveniently made use of, the diurnal motions of the 

 planets may be shown. By substituting a catgut string instead of 

 the thread which suspends the Sun, its motion round its axis may 

 easily be shown. By using a lamp instead of the gilt ball, or placing 

 a candle at a proper height, eclipses of the Sun and Moon, and 

 phases of the Moon, may be explained in a pleasing manner. It is 

 suggested, in order to make the Earth keep its parallelism whilst 

 revolving round the Sun, that a small terrestrial globe with an axis 

 rendered magnetic be made use of; and if still greater accuracy be 

 desired, that a bar magnet be placed according to the present de- 

 clination of the Magnetic needle within a globe ; but such a method 

 does not appear to be necessary. 



I am persuaded that a very amusing and instructive Planetarium 

 on the plan of this may be made, and hope to see one with im- 

 provements. If a method can be adopted by which the planets can 

 be placed at one point, to set out from, in their revolutions, it would 

 be very satisfactory. Perhaps by having different pieces of catgut 

 (instead of one string) to be connected by screws to the rods, this 

 could be accomplished ; but I think there will be some difficulty at- 

 tending the attempt. This Apparatus I propose calling an '< Atmo- 

 spherical Planetarium, or Orrery," as it is put in motion by the state 

 of the atmosphere as respects moisture, in the same way which 

 catgut Hygrometers are. Perhaps some preferable substance to cat- 

 gut may l)e met with ; but I know not of any such. To |)revcnt tiie 

 strings entangling, the apparatus had better be removed in different 

 portions than when connected together. I think it possible that a 

 very eccentric orbit of a Comet may be contrived on the same prin- 

 ciple 



