104: C. A. Steinheil S5hne, Mflnclien. 



6. Critical examination of the polished surfaces with respect to 

 perfection of sphericity by means of standard glasses, imper- 

 fections of the surfaces being indicated by the appearance of 

 Newton's coloured rings. 



By adhering to its maxims the establishment developed rapidly 

 and the following are among its principal achievements: 



1859. Establishment, in conjunction with Professors Kirchhoff and 

 Buns en, of the practical forms of the spectroscope; 



1865. Construction of periscopes and of telescopic objectives with 

 flint front lens (patented in Bavaria), aplanatic lenses and micro- 

 meter oculars: 



1866. Completion of the first type of the aplanatic lens (Bavarian 

 patent of 1866), which in 1867 was awarded a Gold Medal at 

 the Paris International Exhibition: 



1871. Construction of wide angle aplanatic lenses at the instigation 

 of the Austrian ministry of war; 



1872. Astro-photographic objectives; 

 1878. Aplanatic group lenses (patented): 

 1881. Antiplanetic lenses (several patents) ; 

 1885. Panorthic double telescopes (patented): 



1887. The head of the firm was invited by the ,,AcademiedesSciences" 

 of Paris to attend the congress held with the object of dis- 

 cussing the subject of the production of photographic celestial 

 charts. On this occasion Dr. Ad. Steinheil protested against 

 the resolution carried by the majority regarding the conditions 

 which govern the production of correctly delineated charts of 

 constellations. For that resolution limited the conditions, which 

 were to be realized, to aperture, focal length and correction of 

 spherical and chromatic aberration. In pursuance of this con- 

 gress an objective having an aperture of 33 centimeters was 

 ordered by the Astro-physical Observatory of Potsdam and also 

 one of an aperture of 23.5 centimeters, which were completed 

 in September of the year 



1889, and which embodied the conditions laid down by Steinheil. 

 The excellence of this objective led to 



1890, a similar objective of 33 centimeter being supplied to the ob- 

 servatory of Catania in Sicily; and 



1892 a similar objective of 33 centimeter achromatized for the chemical 

 rays, and also a 36 centimeter objective achromatized for the 

 visual rays, both to the Observatory of Upsala. 

 Beside these a great number of objectives of 10, 9V 2 , 9 and 8 

 inches diameter were made. 



A prominent feature is also the manufacture of piano-parallel plates 

 and accurate prisms and, as a speciality, very exact piano-parallel glasses 

 and mirrors of about l / 3 millimeter thickness. 



The following table contains a statistical report of the distri- 

 bution of inland and foreign export during the period 1881 to 1890: 



