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• This obfervation of the fecond limb gives the difference of longitude greater 

 than the obfervations of the preceding limb ; which is to be attributed to the 

 difference of the telefcopes. — The Greenwich tranfit inftrument gives a lefs 

 diameter of the fun than the tranfit inftrument of the obfervatory of T. C. D. 

 and the effeft of this difference of inftruments is to leffen the longitudes de- 

 <luced by the above method from obfervations of the firft limb, and to increafc 

 thofe deduced from the fecond limb. Confequently to ufe this method to moft 

 advantage a mean of refults deduced from obfervations of both limbs ought to 

 be taken. 



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