II. MOLECULAR STRUCTURE. 403 



1799. Four Micrometers, for Astronomical Telescopes. 



F. W. Brcithaupt and Son, Cassel. 



Micrometer divisions on glass, for different kinds of astronomical observa- 

 tion. The one with circular divisions was used by Prof. Sporer, of Anclain, 

 for the observation of the solar prominences at Aden during the total solar 

 eclipse. 



1800. Electro-magnetic Registering Apparatus. 



M. Th. Edelmann, Physico- Mechanical Institute, Munich. 



ISOOa. Stereo-Micrometer. Apparatus used with binocular 

 telescopes, and measuring both angles and distances, for geodetic 

 and astronomical measurements. Both eyes being employed, one 

 measuring, the other observing, position and distance are thus 

 given simultaneously. With stereo -micrometrical photographs of 

 landscapes. Prof. Carl Wenzel Zenger, Prague. 



ISOOb. Positive Eye-piece, with a bright line micrometer, 

 invented by the exhibitor for the purpose of making measurements 

 in the dark. A. Hilger. 



II. INSTRUMENTS FOR DETERMINING THE MO- 

 LECULAR STRUCTURE OF THE HEAVENLY 

 BODIES. 



a. SPECTROSCOPES. 



1801. Spectroscope of Donati, which served him in the 

 observations of the eclipse of the sun, made in Agosta (Sicily) 

 the 20th of December 1870. 



The Royal Institute of " Studii Superiori" Florence. 



With the aid of this spectroscope Donati was able, during the eclipse, to 

 observe the luminous lines of hydrogen. He afterwards constructed a second 

 one, composed of 25 prisms of very great dispersive power. His premature 

 death, however, robbed science of the important observations which would 

 certainly have resulted from so perfect an instrument. 



1802. Amateurs* Star Spectroscope. John Browning. 



This instrument will show the lines in the spectra of stars of the second 

 magnitude, when used with an object-glass only 3 in. in diameter. By de- 

 taching the cylindrical lens, the instrument may be used as a small direct 

 vision spectroscope. 



1803. Spectrum Apparatus, for the observation of the spectra 

 of the fixed stars, planets, and nebulae ; arranged after the spectrum 

 apparatus of Boshkamper (belonging to the Observatory of Ham- 

 burg). Hugo Schroder, Hamburg. 



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