Astronomical Operations at the Pulkova Observatory. 89 



whose diameter is 52 inches, and which has a telescope whose 

 aperture is 5-9 inches, and focal length 74 inches. The nriagni- 

 fying power ordinarily used in this instrument is 215. The ob- 

 ject-glass and eye-glass in each of these instruments are mutu- 

 ally interchangeable at pleasure. 



Beside these, the observatory possesses, 1st, a meridian telescope 

 made by Ertel, whose aperture is 5-S inches, and focal distance 

 102 inches, and whose ordinary magnifying power is 292 : 2d, 

 an instrument for transits in the prime vertical, made by the 

 Repsolds, whose telescope has an aperture of 6^ inches, is 91 

 inches in focal length, and sustains a magnifying power of 263 : 

 3d, a great heliometer of Mertz and Mahler, of Munich, whose 

 aperture is 7^ inches, and focal length 10 feet. Struve has taken 

 upon himself the charge of making observations with the second 

 of these instruments. The first is committed to his assistant, 

 Mr. Peters, and the third to Mr. G. Fuss. 



To finish the enumeration of the principal astronomical instru- 

 ments now in use in the observatory of Pulkova, there remains 

 to be mentioned the great achromatic telescope of Mertz and 

 Mahler, equatorially mounted, whose clear aperture is 14-93 

 inches, and focal length 21*85 feet. The highest power adapted 

 to a wire-micrometer in this telescope magnifies angularly 1822 

 times. This instrument has been employed by Mr. Otho Struve, 

 a son of the director of the observatory, in a review of the north- 

 ern hemisphere, relative to stars of the first seven magnitudes, 

 and to the double stars. 



Toward the close of the year 1841, the third section of the 

 northern hemisphere had been explored, and the number of stars 

 determined in this space, as far as the seventh magnitude inclu- 

 sive, v/as 5275, of which 1194 were of the first six magnitudes, 

 and 4081 of the seventh magnitude. The magnifying power 

 commonly used was 412, while Struve. the father, had adopted 

 one of 198 in his examination of double stars with the Dorpat 

 telescope, whose quantity of light is only a third of that of the 

 Pulkova instrument. In the part of the heavens already exam- 

 ined at this last observatory, there have been found 551 double 

 stars, of which 349 are comprised in the catalogue of Dorpat, 

 and 202 are new. Of these last, 59 are of the first order ; that 

 is, those in which the two stars have an apparent angular dis- 

 tance of less than one second. The catalogue of Dorpat con- 



Vol. xLvii, No. 1.— April-June, 1844. 12 



