310 



Intellweiice and Miscellaiveons Articles. 



Millington was about to deliver a course of lectures on pneuma- 

 tics, and that these would be followed about the middle of April, 

 by a course of lectures on the structure and functions of the hu- 

 man body, by Dr. Birkbeck, the President. 



LXI. InielHsetice and Miscellaneous Articles. 



I 



DESCRIPTION OF A PLANETARIUM, OR ORRERY, ON A NEW 

 PRINCIPLE, PUT IN MOTION BY THE STATE OF THE ATMO- 

 SPHERE. 



IN the year 1824, 1 made a Planetarium or Orrery, on a new prin- 

 ciple, showing the motion of the Earth and Moon round the Sun, 

 and of the Moon round the Earth ; of which invention I observed a 

 notice in the Philosophical Magazine for March that year. I have 

 lately constructed one on the same principle, representing the Sun, 

 an inferior planet (Venus), the Earth and Moon, and a superior 

 planet (Mars), — which I shall describe, referring to the figure which 

 accompanies this paper. The figure is not given as an exact re- 

 presentation as to dimensions, but will, I imagine, with the descrip- 

 tion be found sufficient for those persons who may wish to make a 

 planetarium of the same sort. The principal parts of this machine 

 are the following ; to which may be added rings and hooks for con- 

 necting the parts together. 



A piece of catgut string about fifteen 

 inches in length, A (represented as 

 suspended from a beam in a room), 

 this passes through the round bars or 

 rods B, C, D, and is fastened to them 

 on the under sides by knots with glue, 

 to prevent them from slipping. E, a 

 small bar or rod ; F, a string of catgut 

 about three feet long. G, H, I, J, K, 

 five wooden balls to represent the Sun 

 (which is gilt), Venus, the Earth, the 

 Moon, and Mars. These balls are some 

 suspended by sewing (linen) thread, and 

 some by silk. They might all have been 

 of either of those substances. 



The Sun is hung below the catgut 

 string A. Venus, from one end of the 

 bar l3. The Earth and Moon from E, 

 which is suspended from the bar C 

 (by catgut), and Mars from the bar B. 



In order to balance the three large 

 rods, I make use of flexible copper wire; 



and find a piece wound round spirally, very convenient for the 

 purpose. 



The 



