Mr. PoGSON on the Madras Celestial Survey 91 



Preliminary Reductions. — The catalogues from which 

 the chief mass of fundamental points will be derived are 

 those of Lacaille, Taylor, Weisse's Bessel, and Oeltzen's Ar- 

 gelander. Every available star will however be reduced up 

 to the adopted epoch, from every accessible known catalo- 

 gue, and the whole will be collated, to form the separate lists 

 of zero stars required for the zones of the respective charts. 

 This is unquestionably the most tedious part of the whole 

 undertaking, but far lighter for the southern hemisphere 

 than that which Professor Argelander and his staff must 

 have gone through for the northern portion. Apart from 

 the necessity of such a reduction for the zero points of the 

 survey zones, the complete revision thus afforded of all re- 

 corded positions of southern stars is in itself a ^vork of much 

 importance at the present time. 



Instruments employed and mode of using them. — So long 

 as it remains in my possession, the exquisite five foot Smy- 

 thian telescope, the property of Dr. J. Lee, F. R. s. of Hart- 

 well, originally made for Admiral W. H. Smyth, may be re- 

 garded as the standard instrument with which the survey 

 is intended to be made. In case however of its being re- 

 called, I have had the object glass of the old Madras Transit 

 instrument, 3 94* inches in clear aperture, mounted upon 

 one of Troughton and Simms's universal equatorial stands ; 

 and though inferior in quality to Dr. Lee's telescope, its 

 somewhat larger aperture entitles it to rank as a secondary 

 standard. Dr. Lee has most kindly lent me his instrument 

 ever since the year 1857, and I doubt not that in considera- 

 tion of the important service it will render if employed as 

 proposed, he will, with his characteristic readiness to en- 

 courage every scientific undertaking which gains his appro- 

 val, permit me to retain it on a much longer loan. 



