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For this reason we have applied to all values of 15 //a cos 8 both to the stars of Gill and to those of Newcomb in the same zone, a correction

J (15 /Ua COS S) — 4- 0*.02Ó.

For the rest the proper motions have been taken unaltered from the respective catalogues.

For the purpose of reducing the magnitudes of the stars of Gill to the scale of Potsdam, the magnitudes, as given in the catalogue, have been compared, as far as possible, with those given in Harvard '). In this way the following corrections for the reduction to Harvard, denoted by H — G have been derived for the different classes of magnitudes. They have been slightly smoothed by a curve. By further adding a correction of + om. 17, we got the reductions to the Potsdam scale, denoted by P — G.

m H-G P-G

m m

4.0 to 4.4 + 0.04 +0.21

4.4 to 4.9 —0.28 —O.II 5.0 to 5.4 — 0.40 — 0.23

5.5 to 5.9 —0.44 —0,27 6.0 to 6.4 — 0.46 — 0.29 6.5 to 6.9 — 0.47 —0.30 7.0 to 7.4 —0.41 —0.24 7.5 to 7.9 —0.27 --O.IO 8.0 to 8 4 — 0.14 4- 0.03 8.5 to 8.9 + 0.01 + 0.18 9.0 to 9.4 + 0.14 + 0.31 9.5 to 9.9 +0.21 -f- 0.38

As far as the magnitudes for the stars used were given in the Harvard catalogue, these have been taken, after ha ving added a correction of + om.i7. For the rest the correction P — G was applied to the magnitudes.

Stars of Auwers.

For these stars the proper motions as given in the catalogue of Auwers have been corrected for precession, adopting that of Newcomb. For this purpose values of km and A» have been used in accordance with those taken in Publ. 9 of the Astron. Lab. of Groningen (pag. 4) i. e.

') Annals of the astron. observatory of Harvard college, vol. XXXIV, which according to page 53 of this catalogue, has been joined as closely as possible to the Harvard Photometry (vol. XIV, Pickering I according to the Publ. of Potsdam).

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