696 PROGRESS OF ASTRONOMY FOR 1891 AND 1892. 



able that in the .second series (those with an odd degree at t)ie center) 

 there shouhl be two or three exposures. 



(9) To make it possibh' to pass nniformly and with certainty from 

 Argelander's ninth magnitnde to the eleventh magnitude desired i'or 

 the negatives of the photographic catalogue there will be distribnted 

 among the observatories line wire-gauze screens, absolutely identical, 

 which, when jjlaced over the object glass of the telescope will dinunish 

 the magnitude of a star by two units (adopting the coefficient 2. r>r2 tor 

 the ratio between two consecutive magnitudes), li^ach observatory will 

 from time to time mnke type negatives of certain specified regions. 



(10) The committee suggests forty minutes as the length of exposure 

 of the i)liites for the chart (the series of c?'ew declinations) under the ordi- 

 nary atmospheric conditions of Paris, and with the Lunnere plates used. 



Thecomndtteeon metallic screens will fnridsh the Messrs. Henry with 

 a screen with which they will determine the time / for obtaining the 

 eleventh magnitude stars of Argelander's scale. Then for each obser- 

 vatory provided with an identical screen, the ratio 40 :t will be the factor 

 by which to multiply the time of exposure necessary to secure satisfac- 

 tory images of eleventh magnitude stars, in order to obtain the proper 

 ex})osure for the chart ])lates. 



(11) The ([uestions of the number of reference stars for each nega- 

 tive for the catalogue, the choice of the stars, and the necessary steps 

 to secure meridian observations are referred 1o a special committee, con- 

 sisting of Messrs. Auwers, Bakhuyzon, Chiistie. Elh^ry, Gill, Kapteyn, 

 and Loewy, with lull i)oweis. 



(12) As soon as convenient each ol)server will prepare, «u- will have 

 prej)ared by any observatory or bureau lie may select — 



{(() Measures of the i)Osition of each star on the catalogue referred by 

 rectilinear coordinates to the nearest lines of the '" rr^mii." 



{h) Measures necessary for the detenniuation oi" the stars' magnitudes. 



The different observatories will publish the separate results of these 

 measures and the Permanent Comndttee will undertake their reduction 

 as soon as a sufficient nund)er(d' meridian observations of the reference 

 stars is at hand. 



(l.'i) The work upon the chart will commence at each observatory as 

 soon as the metallic screen reducing the stars by two magnitudes is re- 

 ceived, involving probably a delay of two months. Each observer may, 

 however, begin before receiving the screen if he is contidentthathe can 

 get all stars of the eleventh magnitude upon the catalogue plates. 



(14) Without adopting a formal resolution, the committee would 

 recommend as a separate and personal investigation, that a special series 

 of negatives with long- exposuresbemadeof theregiou neartheecliptic 



