120 [Assembly 



lar form, with a revolving dome of 12 feet diameter, which is 

 moved at pleasure by a crank with rack and pinion.- The hem- 

 ispherical top of the dome, moves upon an iron ring 12 feet di- 

 ameter, cast in one piece, and turned in a lathe on the upper side, 

 upon which the grooved wheels run. The observing chair 

 with the observer, are carried round with the dome, which is 

 another new feature in this domestic observatory, and it is found 

 to answer admirably. The building is of brick, with an under 

 cellar ten feet below the surface of the ground. The instrument 

 is placed upon a pier of brick encased in iron, three feet in di- 

 ameter, which stands on three beams built into the walls of the 

 house, about three inches below the floor of the observatory. 

 The great steadiness obtained by. this arrangement, is a matter of 

 surprise to practical astronomers, and contrary to their predic- 

 tions. 



The opening in the dome gives a view from the horizon to the 

 zenith, and is closed or opened by rack work, with a crank, al- 

 ways at the command of the observer, without leaving his seat. 



A, c. 



