II. MOLECULAR STRUCTURE. 405 



1806e. Photographs of Hilger's Stellar and Solar 

 Spectroscope. A. Hilger. 



4552. Photographs representing various Scientific 



Instruments in the Observatory of the Collegio Romano, Rome. 



Padre Secchi, Director, Rome. 



No. 1. Spectroscope applied to the refractor of Merz, provided with a net- 

 work by Rutherford. 



No. 2. Spectroscope Avith network, applied to the refractor of Merz, with 

 the cover adapted to the plate of the network. 



No. 3. Spectroscope with five prisms, with double passage of the ray by 

 reflection, and with automatic movement to bring within the eyepiece the 

 various dispersed rays. 



No. 4. Spectroscope with three angular prisms, and one with direct vision, 

 enclosed in the collimator. 



No. 5. Large objective prism of Merz, of 6 inches, for the'spectrum analysis 

 of the stars. 



No. 6. Meteorograph of Padre Secchi. 



No. 7. Curves traced with the meteorograph. 



4555. Photographs representing the Daily Drawings 

 of the Solar Chromosphere, made by the spectroscope of 

 Professor Lorenzo Respighi. 



Prof. Lorenzo Respighi, Director of the Royal Observatory 

 of the Campidoglio, Rome. 



On the 26th October 1869, at the Observatory of the Campidoglio, the spec- 

 troscopic observation and the daily representation of the chromosphere on 

 the solar horizon were for the first time undertaken, and this work has been 

 regularly continued up to the present time. The instrument used in these 

 observations is an equatorial by Merz, with telescope of 4 inches aperture, to 

 which is applied a spectroscope with direct vision, by Hoffmann, with five 

 prisms, with circle of position to fix the place of the various parts of the 

 chromosphere and of the protuberances. Notwithstanding the small dimen- 

 sions of the instrument and the moderate dispersion of the spectroscope, the 

 chromosphere and the protuberances are clearly exhibited even in their 

 smallest details. 



The Photographs I., II., III., IV., and V. represent 140 drawings of the 

 chromosphere made with this apparatus by Professor L. Respighi. 



d. STELLAR PHOTOMETRY. 



18O7. Astronomical Photometer. Designed by Professor 

 Thury. 



Geneva Association for the Construction of Scientific In- 

 struments. 



The apparent brightness of a heavenly body seen in the telescope is gra- 

 dually reduced by the movable diaphragm placed before the objective, and 

 if necessary by the interposition of one or two dark mirrors placed behind the 

 eyepiece in the square box, which is exposed with the diaphragm. The light 

 is gradually reduced until the object is no longer visible. The aperture of the 

 diaphragm is then shown upon a dial placed under the eye of the observer. 



The full description of this apparatus is to be found in the "Archives de* 



Sciences physiques et naturelles de Geneve," 1874. 



