ASTRONOMY. 147 



ate the necessary funds for the Washington Observatory. The business 

 of the permanent committee is transacted through an executive bureau, 

 consisting of Admiral Mouchez, president; Christie, Duner, Janssen, 

 Struve, and Taccliini, members, and Gill, Loewy, and Vogel, secretaries. 

 It is expected that meetings of the permanent committee will be held 

 every three years, though they may be called more frequently if found 

 desirable. Before adjourning, the Congress elected also a special com- 

 mittee, to occupy itself with the application of photography to astron- 

 omy other than the construction of a map, acting in concert with tlio 

 permanent committee. Messrs. Common and Janssen were requested 

 to take charge of this matter. They have communicated by circular 

 with all who are likely to be interested in this work, and propose to call 

 a meeting at Paris, and form a committee for the consideration of the 

 best means of carrying out the plan suggested by the Congress. 



As many preliminary experiments are necessary in arranging details, 

 special subjects of investigation have been referred to different astron- 

 omers. For instance, the study of the proper form of reticule, to Vogel ; 

 photographic magnitudes, to Struve and Pickering; optical deformation 

 of images, to Struve; study of three or four stars nearly in a straight 

 line, embracing an angular distance of about 1 degree, and photographed 

 necessarily at the center and corner of a plate, to the observatories of 

 Algiers, Leyden, Paris, Pulkowa ; distortion of the sensitive film, to Al- 

 giers, Meudon, Potsdam; curved plates, Christie; orientation of the 

 plates, the Cape, Paris; measuring apparatus, to a special committee; 

 formula for the preparation of the plates, Abney, Eder; the effect of 

 colors of the stars upon the photographic magnitude, Dun6r. 



The permanent committee has published, through the Paris Academy, 

 three reports: the first, a full account of the Congress held in April, 

 1887; the other two, "bulletins," containing correspondence and results 

 of the preliminary investigations. These papers are of great importance 

 in the proposed photographic work, but they can hardly be reviewed 

 satisfactorily here. The most extensive are: "Note sur I'application do 

 la photogrnphie aux mesures microm^triques des dtoiles, T.-N". Thiele; 

 De I'influence des dur6es de la pose sur I'exactitude des photographies 

 stellaires, J. Scheiner ; Travaux preparatoires effectues a I'observatoiro 

 de Potsdam, Vogel; Expose do la methode parallacticiue de mesure, — 

 reduction des cliches, J. C. Kapteyn; llecherches faites a I'observatoiro 

 de Harvard College sur les resultats photometriques, E. C. Pickering; 

 fitendue dn champ des cliches photographiques de I'observatoire de 

 Paris, :\rM. Henry." 



It is strongly recommended that the i)lates bo measured at a central 

 bureau established in the neighborhood of Paris. 



Professor Pritchard having undertaken, for the photographiio com- 

 mittee of the'lloyal Society', an examination of two silvcr-onglass mir- 

 rors of the same aperture but of very difterent focal h'ngths, with a \ lew 

 of ascertainnig the practical effects of focal length on the ph()t()grai)iiic 



