174 



those limits; when, the Epheoieris being corrected, it can 

 be observed on the meridian in the usual way. This has 

 already been tested in finding some of the old Asteroids, 

 using for our Ephemerides Hind's Supplement to the Nau- 

 tical Almanac. 



In our ordinary work, as we observe all stars visible, the 

 limit being 13-14 magnitude, it is usually impracticable to 

 observe a zone of greater width than 10' or 12' ; and within 

 these limits, it is not unusual to find more than 200 stars in 

 one hour of Right Ascension. The magnitudes of the stars 

 observed are recorded on the Chronograph, by striking a 

 certain number of dots for each magnitude. This, how- 

 ever, is not absolutely necessary, since the assistant in 

 reading the Declinometer scale records, at the same time, 

 the number of the star and the magnitude, and, to guard 

 against error, occasionally the time of transit. 



In order, however, that the apparatus may be complete 

 within itself, we propose to attach a mechanism so that the 

 observer can record, with type or otherwise, the magnitudes 

 in their regular order. 



In ca?e we wish to extend our observations over more 

 than one hour of Right Ascension, we loosen the clamp 

 screw (§•), fig. 1, and slide the whole apparatus carrying the 

 pencil, on the post e ; the end of the connecting rod {/) 

 being raised up and dropped on another pin. These chang- 

 es can all be made in less than one minute. 



In our zone work with this apparatus, we have ob- 

 served and charted 300 stars in a single hour. But gene- 

 rally we consider 200 as the maximum number that can 

 conveniently be observed in that time ; since, in the latter 

 case, greater accuracy can be attained, which is more to be 

 desired than multiplicity of observations. 



Having given a general outline of the plan adopted in 

 mating charts of zone stars, it may now be desirable to 

 state some of the possible advantages resulting from the 

 use of this method. 



