to the Legislature of the State of JYew Tork. 265 



render it visible, and another to keep in the line of observation and 

 to mark the point where it terminates. 



The usual means should be employed to ascertain the fact that 

 there is nothing about the place by which the needle may be at- 

 tracted. 



Within the limits of the State of New York, the following method 

 is practicable, and, if carefully conducted, will give a meridian as 

 true, for the present purpose, as can be expected from the other 

 prescribed methods. 



Alioth and Gamma Cassiopeice pass the meridian at the same 

 moment, within two seconds of time, the one below and the other 

 above the pole. If then the line be accurately observed in which 

 they appear when in the same vertical, that line will be the true me- 

 ridian, without an appreciable error ; and as the difference between 

 the changes in right ascension of these two stars is only 13 hun- 

 dredths of a second annually, it will not sensibly affect the accuracy 

 of the rule and its practical results for many years. 



At some distance beyond our north bounds these stars will so 

 nearly approach the zenith as to render the observation inconvenient, 

 with a plumb line, but not with a transit instrument at any place far- 

 ther to the north. The observation will be practicable either way, 

 as far south as the 35th degree of north latitude, whence Gamma 

 Cass, will be seen at its lowest depression, somewhat less than five 

 degrees above the horizon. In latitude 43°, AUoth will come with- 

 in 14 degrees of the zenith, and Gamma Cass, within 13 degrees of 

 the horizon, at the time when the observation is recommended to be 

 made, which is from the middle of May to the 1st of June. On the 

 15tb of May, the stars will be on the meridian at about 19 minutes after 

 9 o'clock in the evening, apparent time, and about four minutes ear- 

 lier on every succeeding day. 



Gamma is the middlemost of the bright stars that compose Cas- 

 siopeia's chair. 



The meridian line being thus accurately and permanently fixed, 

 (and this ought to be considered as an indispensable appendage to 

 every college and academy,) observations should be made on it at 

 least once in every year, in order to ascertain the difference between 

 it and the magnetic meridian. For the sake of uniformity, let this 

 be done in October. 



These observations should be made early in the morning, for it 

 is well known that the variation of the needle will be increasedj 



Vol. XXV.— No. 2. 34 



