observed with the Great Achromatic of Fraurihqfer. 81 



within reach of my telescope, in order to observe which among 

 them were double. I was in hopes that by making this sur- 

 vey of the Heavens in a regular manner I should increase the 

 number of double stars, gain perhaps more positive know- 

 ledge of the method of distinguishing those stars which are 

 physically and optically double, and finally deduce some gene- 

 ral views respecting the manner in which these stars are distri- 

 buted throughout the celestial vault. 



It is under the equator alone that the whole vault of the 

 Heavens can be perceived, owing to the rotation of the earth, 

 while at both the poles one-half only can be seen. In the la- 

 titude of Dorpat 121 \° of the Heavens can be observed from 

 the North Pole to about 31 1° south of the celestial equa- 

 tor. But the south stars rise too little above the horizon 

 to be examined with any success, even through a powerful 

 telescope ; for at this small height the lower strata of the at- 

 mosphere produces a tremulous motion in the image. I re- 

 solved in consequence that I would extend my survey only 

 to 105° from the pole, or 15° south of the equator. In this 

 .space the lowest stars were still at a height of 16J° above 

 the horizon in their meridian passage. I divided this space 

 into 12 zones, according to their distance from the celestial 

 pole, and I performed my reviews by zones. All the stars 

 up to the eighth magnitude, and the most brilliant of the 

 ninth which can be discovered with the finder of the instru- 

 ment, were brought one after the other into the field of the 

 telescope to discover which of them were double. As soon as 

 a star was known to be double, its position was determined by 

 the reading of the index of the two circles of the instrument, 

 as well as by the clock regulated to sidereal time, and a short 

 description of the star, according to its class and magnitude, 

 was written in the register. When a magnifying power of 214, 

 generally employed, made us only suspect that a star was 

 double by showing itself under an elongated form, a stronger 

 magnifying power of 600 times was employed to decide the 

 point. 



The number of stars thus passed in review were computed 

 at 120,000. I have collected in a catalogue, which will be 

 published, all the double stars thus found, including those 



VOL. IX. NO. I. JULY 1828. F 



