and positions of 4;SS double and triple stars, ^c. 51 



No. CCCCXLIV. R. A. 3^ 58' ; Decl. 22« 38' N. 



Nova; 

 Double ; 9th and 9^ magnitudes. 



Passy ; October 16, 1825 ; Seven-feet Equatorial. 



Diff! = o«^^2 1 Extremely difficult. 



Position = 84° %' sp 

 Distance = 6". 301 



5 Obs. 

 5 Obs. 



Neither star bears sufficient illumination. Night foggy. 



Between this night and the 22nd of October, when the observatory at Passy was 

 broken up, unfavourableness of the weather prevented me getting a second series 

 of observations. 



axis ; the cones however of the horizontal axis being firmly soldered and pinned to a 

 shoulder projecting from the centre-piece, are not separable from it : the level of 

 the axis is supplied with a silver scale, each division of which is equivalent to one 

 second. In the focus of the object-glass are seven equi-distant wires, the equatorial 

 interval between any two of them being about 20 seconds of time : on each side of 

 the meridian wire, and at equal distances from it, are two others, so placed that the 

 pole star shall pass from it to either of them in two minutes, for a purpose explained 

 in the Memoirs of the Astronomical Society (vide Vol. I. page 238) ; applicable to 

 each side plate, is an apparatus for regulating the quantity of light projected from 

 the lamp upon the wires. The side plates are similar to those belonging to my 

 Four-feet Transit Circle, and which (I believe) were described in Rees's Encyclo- 

 paedia, when the instrument was the property of Mr. Groombridge. A second 

 level for the horizontal axis, a spare one for the altitude circle, and a second wire- 

 plate furnished with spiders' lines are at hand, and are ready for immediate use, 

 should accident sustained by any of the first set, render them unfit for service— a 

 reserve which no traveller should neglect ; lest also any of the screws by which the 

 various parts of the instrument are connected should be lost, a few additional ones 

 placed in the box are not, (as I have found by experience), without their use. 



The object-glass was made by Mr. Tulley, and originally belonged to the 

 Westbury Circle : its clear aperture is 2.7 inches, its focal length is 43 inches; with 

 a magnifying power of 300 it defines a Lyrae, Arcturus and Aldebaran, perfectly 

 sharp and round; separates very distinctly the close stars of yLeonis, t Bootis, and 

 ^Orionis; whilst with 150 (the commonly used power) under favourable circum- 

 stances, the small star south preceding Polaris, is sufficiently visible to enable the 

 observer to take its transit, with considerable precision. 



The instrument is mounted on stone piers, and has retained its meridian position 

 extremely well ; fifteen months' experience has shown, that whilst the maximum 

 error, to which the mean of a single series of observations of any star south of the 

 zenith of my observatory, does not exceed 4-tenths of a second, often, very often, the 

 result of a single set will not deviate 2-tenths from the true right ascension. When 

 the pole star is steady, its transit over the wire may be determined to one second. 

 Thus much for its utility. 



As for its portability : the transverse axis, the telescope tubes, and the altitude 

 circle, are included in a box 29 inches long, 14 inches broad, and 6| inches deep. 

 The three levels, the spare wire-plate, the light regulating apparatus, the lamp, &c. 

 are lodged in a case 27^ inches in length, i\\ in breadth, and 3! in depth. The 

 side plates, with their appendages of nuts, screws, &c. are contained in a box 13I 

 inches long, y\ inches broad, and 7^ inches deep; and the tout ensemble is well accom- 

 modated under the seat of my travelling carriage. (The measures are all exterior.) 



. Passy; October 2Z, 1S25. 



