ASTRONOMY. 147 



ate the uecessary funds for the Washington Observatory. Tlie business 

 of the permanent committee is transacted through an executive bureau, 

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

 Struve, and Tacchini, 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 the 

 permanent committee. Messrs. Common and Janssea 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 i^hotographic 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 de 

 la photographic aux mesures micronnStriques des etoiles, T.-N. Thicle ; 

 De I'intluence des dur^es de la pose sur I'exactitude des photographies 

 stellaires, J. Scheiner; Travaux prdparatoires effectues ;\ I'observatoiro 

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

 r(5duction des cliches, J. C. Kapteyn; llecherches faites a I'observatoire 

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

 fitendue du champ des cliches photographiques do I'observatoire de 

 Paris, ]\IM. Henry." 



It is strongly recommended that the plates be measured at a central 

 bureau established in the neighborhood of Paris. 



Professor Pritchard having undertaken, for the photographiic coiii- 

 niittee of the Royal Society, an examination of two silver-onglass mir- 

 rors of the same aperture but of very different focal lengths, with a view 

 of ascertainnig the practical eftects of focal length on the photogra[)liic 



