ASTRONOMICAL OBSERVATOlilES. 463 



The new observatory erected by thelioyal (iovernment iu the neigh- 

 borhood of Potsdam, and whose buildiuos and eciuipinents are now 

 nearly completed, has for its fundamental purpose the investigation of 

 the composition and movements of planetary bodies by means of spec- 

 tral analyses and continued records of the events on their surfaces. 



The observatory occupies the so-called Telegraphenberg, formerly a 

 station of the optic telegraph line ''Berlin-Cologne," situated south of 

 the city of Potsdam, upon the east bank of the river llavel, and about 

 li Idlometers (0.8013 mile) from the railroad depot. On the summit, 

 im igs ^y_ of Berlin, in north latitude 52^ 2V 50", 04 meters (318 feet) 

 above the level of the sea and 04 meters (200 feet) above the level of the 

 river Ilavel, is located the principal building, supi)lied with three mov- 

 able cupolas, one of 10 and two of 7 meters (33 and 23 feet) diameter, 

 respectively. Around this are physical, chemical, and photographic 

 laboratories, workshops provided with a dynamo-electrical machine, 

 office, janitor's dwelling, and some other rooms for observations and 

 collections. Along the gentle northeast slope are three dwelling-houses 

 for the scientific staff and the messenger; farther down, close to the 

 entrance of the lot and 20 meters (65.6 feet) below the main building, 

 lies the well, accessible for observations down to the level of the river 

 Havel, the building of the water-works, a shop for the preparation of 

 oil gas, and a dwelling-house for the machinists. 



The observatory is surrounded by a tract of woods which forms a 

 desirable protection against terrestrial radiation and at the same time 

 serves as a condenser of atmospheric humidity. 



This and the adjacent tract of land are the property of the Crown, 

 and thus unobstructed possession for all times is secured for the ob- 

 servatory reservations, now amounting to nearly 17 hectares (42 acres). 



The principal instrument of the observatory is a refractor of 0.298'" 

 (11.7 inches) aperture and 5.4™ (17.7 feet) focus, made, together with 

 auxiliary apparatus of spectroscopes and helioscopes, by H. Schroder, 

 of Hamburg; parallactical mounting and micrometers by A. Repsold 

 & SoHNE. It is used in plain astro-physical v-ork, but i)rincipally for 

 the observation of fixed stars, spectra of uebuhne, and for the study of 

 planetary surfaces. Exclusively for solar observations it is i)roposed to 

 use the second refractor, made by II. Grube, of Dublin, with a parallac- 

 tic telescope of 0.207'" (8.1 inches) aperture and 3.4'" (11.1 feet) focus, 

 and also a Steiniieil telescope of 0.135'" (5.3 inches) aperture and 2.16"^ 

 (7 feet) focus, with parallactic mounting by Pistor »& Martins. This 

 was formerly used by Professor Sporer, of Anclam, in his solar ob- 

 servations. 



Furthermore, for regular photographic work of the sun a special 

 heliograph is to be employed, of which now only exist the optical parts, 

 made by H. Schroder, an achromatic objective of 0.16'" (0.3 inches) 

 aperture and 4'" (13 feet) focus, together with ocular magnifying glasses, 

 and of 0.25'" (0.8 inches) diameter. 



