Royal Astronomical Society. 1 4-9 



by clock-work, the moving power of which is a water-mill, regu- 

 lated by " Siemen's Chronometric Governor." This is so success- 

 fully applied, that the rate of the hour-circle is not sensibly altered 

 by clamping the polar axis to it. When the hour-circle is properly 

 adjusted, the instrument reads off right ascensions at once *. The 

 polar axis, which is of wrought iron-plate, is very massive and stiff. 

 The weight of the whole instrument is between 70 and 80 cwt. 

 This keeps all steady, even in very hard gales. The instrument is 

 abundantly supplied with eye-pieces and micrometers. The stiff 

 frame and large circles were evidently designed by Mr. Airy to 

 supply a peculiar power to the instrument. In ordinary mountings, 

 great accuracy is not to be expected when the star of reference is 

 more than a few minutes distant from the object compared. The 

 screw of the micrometer is not to be relied u])on for larger spaces, 

 and the circles, though sufficient for finding and identifying, are 

 seldom intended for accurate measures. Stars of comparison can, 

 indeed, generally be found which are contained in some of the special 

 and extended catalogues, but such stars can only be considered to be 

 roughly known, and in many cases fail altogether. The Liverpool 

 equatoreal is intended to measure hy its circles intervals of a few 

 degrees, with as much accuracy as the average stars of our extensive 

 catalogues possess, and thus to give excellent places by reference to 

 well-known stars. 



Mr. Hartnup has made some observations to test the powers of his 

 equatoreal in this respect. The observations of y, a, (3 Aquilse, of 

 a and /3 Lyrse, of Castor and Polluxf, show satisfactorily, that within 

 such limits as these the instrument will measure differences of right 

 ascension and north polar distance almost, if not altogether, as well 

 as can be expected from the best meridian instruments. 



Mr. Hartnup further remarks, that the instrument keeps its ad- 

 justments steadily, which seems to show that it is not only firm in 

 itself, but, also, that it rests on a sound foundation. The observa- 

 tions by Mr. Hartnup, of standard stars in all parts of the heavens, 

 are not sufficiently numerous to yield a safe estimate of the probable 

 error of a single independent determination, but it is evidently very 

 small, even for stars at 6^ from the meridian. 



Mr. Bishop's Ecliptic Charts, from Observations at the South 

 Villa Observatory. 



Our treasurer, Mr. Bishop, has lately published the first hour of 

 an ecliptic chart for the epoch 1825. This contains all the stars to 

 the 10 mag. inclusive in a zone of 6° of latitude, 3° on each side the 

 ecliptic. The scale is 1'2 inch to 1°, which gives a clear and open 

 map. The execution is very good. 



In the notice which accompanies the chart Mr. Bishop says, " It 

 is the first of a series of twenty-four charts, which I hope to pub- 

 lish. . . . The discovery of planets is materially facilitated by mapping 

 down the stars within a few degrees on each side the ecliptic ; 



* This contrivance is peculiar to the equatoreals of Cambridge and 

 Liverpool, and in some researches is of great convenience. 



t These observations are given in detail in the accompanying memoir. 



