240 A NEW METHOD OF 



-c -When these adjustments are made, there is no difficulty within the 

 northern tropics in bringing the instrument into the plane of the meridian. 

 The small altitude of Polaris, renders almost the first adjustment by that star 

 unsusceptible of any further correction ; and it seldom happens that some 

 distant object may not be found intersected by one of the wires, which may 

 always be referred to as a meridian mark. To adjust the instrument by Pola- 

 ris, the observer should have a chronometer, whose rate is uniform and well- 

 determined, and he may, if he knows the equatorial interval between the 

 wires, calculate the exact instant it should intersect the first and second 

 wires, which will prepare him for the final adjustment to the central wire. 



The transit instrument is the most perfect that has been invented for 

 the improvement of astronomy. Instruments for measuring angles, no effort 

 of art can render perfectly free from errors of centering, division, &c. But 

 the transit instrument is not susceptible of any instrumental error that may 

 not be obviated. When the instrument is accurately adjusted to the meri- 

 dian, it will be advisable for the beginner to select from the catalogues, those 

 stars which he thinks best adapted, allowing an interval of at least S"". or 4™. 

 between each. He should make a list of them under the heads of their names. 

 Right ascensions for the beginning of the year, and their declinations and 

 altitudes ; since by means of the computed altitudes, the instrument is elevat- 

 ed to the same altitude on the circle, and he will find the star to be observed, 

 in the field view of the telescope. Having observed the transit of the first star, 

 the difference in right ascension of those that follow, will indicate nearly the 

 time that will elapse before the second or third star may be expected to ap- 

 pear in the field view. 



When the observer becomes accustomed to the instrument, and expert in 

 directing it, and in noting the times of transit, he may then observe the tran- 

 sit of as many stars as can be done conveniently, within a given distance from 



