to the Legislature of the State ofJVew York. 261 



According to Dr. Brewster's formula for finding the mean tempe- 

 rature of a place, that of Albany is 50-3191°. 



The Regents, sensible of the value to science and to the whole 

 landed interest of the State, of a record of the variations of the nee- 

 dle from year to year, have addressed a circular to the Colleges and 

 Academies, requesting them to make observations upon this point, 

 and to attain accuracy and uniformity in the results, the Chancellor 

 has furnished a formula for establishing a true meridian, and the most 

 important particulars to be regarded in observing, between it and the 

 magnetic meridian. 



This circular being drawn up with great judgment and ability, and 

 being of general as well as local interest, we now republish, as being 

 the most effectual mode of expressing, at once, our good will to the 

 very important object in view, and of giving the circular the range of 

 tliis Journal. 



An indispensable prerequisite is to have a true meridian establish- 

 ed, indicated by fixed and permanent monuments. The manner in 

 which this is to be done, in order that it may be accurately establish- 

 ed, requires special directions. 



In years past, a rule has been prescribed for obtaining an approx- 

 imate meridian, supposed sufficient for common purposes ; that is, 

 to take the direction of the pole star when it is in the same vertical 

 or perpendicular line with epsilon ursce majoris, called Alioth, that 

 is, the first star in the tail of the Great Bear, or the one next to the 

 four most conspicuous in that constellation. This rule was once 

 correct, but it is more than a century past : since that, the interval 

 between the time when these two stars are in the same vertical, and 

 the time when the pole star is in the meridian, has been gradually 

 increasing, on account of the greater annual increase of the right 

 ascension of the pole star than that o( Alioth. Still some, not aware 

 of this fact, have continued to prescribe the ancient rule. Others 

 bave calculated the interval for a certain period of time, without ad- 

 verting to the changes which would occur in succeeding periods. 

 In order to practice on this rule with accuracy, calculations must be 

 made for the time when it is adopted, and for this purpose the fol- 

 lowing formula is given as an example, adapted to the beginning of 

 this year and a medium latitude, which will give a result sufficiently 

 accurate for every part of our state, and which may be adopted in 

 practice without producing a sensible error for several years, for the 

 purpose now contemplated. 



