Dr. Pearson's Introduction to Practical Astronomy. 1 39 



In §. LXIV. our author gives a description of the Transit circle, 

 by Troughton. This description is accompanied by an admirably 

 executed plate. 



After a Section explaining the method of reducing the apparent 

 to the mean polar distance, the author gives the description of the 

 Altitudeand Azimuth Circle, by Ramsden, which is placed at Palermo. 

 The observations of 7646 stars, forming Piazzi's Catalogue, were 

 made with this instrument. 



In Section LXVII. we find an account of the Westbury Circle, by 

 Troughton. 



In §. LXVIII. the author describes an Altitude and Azimuth in- 

 strument in his own possession. This instrument was constructed 

 by Troughton, but divided by Thomas Jones while its maker was 

 an invalid. As it appears to be the largest instrument of the kind 

 ever made by this eminent artist, it also seems the most com- 

 plete. 



Section LXIX. treats of a new instrument, contrived by a well 

 known practical astronomer, Captain Kater, the intention of which 

 is to do away with the necessity of a level or plumb-line in the ad- 

 justment of a Vertical Circle, or Zenith instrument • the utility of 

 which has been differently spoken of in different observatories. 

 But the contrivance deserves further trial ; and the description here 

 given will enable any instrument-maker to construct it either in the 

 horizontal or vertical form. 



In §. LXX. our author describes the uses and construction of the 

 portable Altitude and Azimuth instrument, and introduces a Table 

 of formulas required in the solution of Spherical triangles, which is 

 essential in the use of this instrument. 



Section LXXI. makes us acquainted with a very portable Altitude 

 and Azimuth instrument of the author's own contrivance. 



In §. LXXII. we find a detailed account of the next principal in- 

 strumentsin the Greenwich Observatory; the two great Mural Circles, 

 by Troughton and Jones. 



The next Section contains an account of two very curious circular 

 instruments, on the repeating principle, by the late eminent artist 

 Reichenbach. To the English reader these are more matters of 

 curiosity than anything else ; because, notwithstanding the great 

 ingenuity displayed in their construction, we conceive them to be 

 liable to give uncertain results when compared with our own more 

 perfect instruments. 



In the next two Sections are described the constructions of two 

 Repeating Circles, one by Troughton, and the other by G. Dollond. 



The account of the Equatorial, another important instrument in 

 an observatory, is contained in §. LXVII. and §. LXVIII. 



In §. LXXIX. and the three following Sections is contained the 

 account of Zenith instruments. Of these there are two kinds. In 

 the first the telescope itself moves through a small angle from the 

 vertical, and in the second the telescope has no angular motion, and 

 the means of measuring a small angle from the zenith is contained 

 in the telescope itself. The first of these have been termed Zenith 



T 2 



