175 



Every one will at once see, that a series of charts, even 

 in the condition in which they are taken from the cylinder, 

 will be of great value to the observatory in which they are 

 made. For, after being numbered and filed, they become 

 so many maps, although the width does not exceed 10 min- 

 utes of arc. But obviously they can be made of greater 

 service, with but little additional labor, by transferring 

 contiguous zones to one sheet. This is easily accomplished 

 by merely pricking through the paper, with a series of 

 points which shall at once indicate the magnitudes. 



In case we wish to search lor Asteroids, we believe much 

 labor can be saved, and equal if not greater facility afford- 

 ed in their discovery. For, suppose we have already com- 

 pleted a series of charts for one hour of right ascension, 

 and one degree declination, it is only necessary to observe 

 and map the same zone, or any portion of it ; when it is 

 readily seen, should there be any Asteroid in that region 

 which was not there when the former charts were made, it 

 will at once be detected. 



The objection may be offered, that with the ordinary me- 

 ridian instruments, we do not have optical power sufficient 

 to detect these faint bodies. Granting this to be the case, 

 it does not affect the principle of the method, for we can 

 use the apparatus with an equatorial of any size. In the 

 latter case, we would clamp the Telescope securely in the 

 meridian, and, attaching an arm to the declination axis, at 

 once connect our apparatus in the same manner as with 

 the trausit. Slow motion in declination can now be given 

 to the Telescope with the tangent screw, and the width of 

 the zone limited by employing any mechanism suitable to 

 the instrument. These minor details, of course, will be 

 arranged by the observer, as circumstances require. We 

 know that an equatorial can successfully be used in differ- 

 ential work, by this method, as has been abundantly verified 

 in the use of the Cincinnati equatorial, which has an aper- 

 ture of 12 inches and focal length of 17 feet. 



