168 



being called the " Declinometer," an account of which will 

 be found elsewhere. 



Perhaps nothing is more desirable at the present time, 

 than accurate Ecliptic Charts of all stars down lo the 14th 

 magnitude. We already have the Charts of Chacornac, 

 Argelander and others, which are of great value in the 

 search, for Asteroids ; but were these charts filled out, as 

 it were, with stars of a higher order of magnitude, it would 

 greatly enhance their value for this purpose. 



All standard charts, that have heretofore been construct- 

 ed, have been made by laying down the positions of the 

 stars, as given by a catalogue previously formed. This, of 

 course, is an extremely difficult and tedious task. It seemed 

 to me that much time and labor might be saved, provided 

 we could make an accurate map at the game time that we 

 observed for exact positions. This result we have suc- 

 ceeded in accomplishing by means of easy and simple me- 

 chanism, a description of which will be given in this con- 

 nection. 



In the cataloguing cf zone stars with the Olcott Meri- 

 dian Circle, during the past year, I found it desirable to 

 have some contrivance by which we could observe the 

 same zone, star for star, on a subsequent night. In order 

 that we may be understood, we add that the clamp arm for 

 giving slow motion to the Telescope in zenith distance, is 

 moved by a screw pressing against its lower end, one revo- 

 lution of the screw being about 6'. That we might get 

 more rapid motion, an extra cog wheel was made to drive 

 one fastened to the screw. To the axis of this new wheel 

 was attached two cylindrical pulleys, each carrying a small 

 weight suspended by a cord wound on the surface of the 

 pulley. The width of the zone was then regulated by the 

 length of the end left free to move. 



It was found that with this contrivance (although we had 

 the play between the two cog wheels), we could follow the 

 same zone with a deviation of less than 5". Were the 



