44 Mr. William Galbraith, on some 



a good instrument with these appendages, and was long 

 so used, has, at last, given place almost universally to the 

 circle which by means of verniers reading round the whole 

 circumference destroy by mechanical means, probably, the 

 small incidental errors inseparable from materials and 

 workmanship however excellent both maybe. "With all 

 the care that could be employed, errors to the amount of 

 20" or 30" were known to exist in the observations of some 

 of the continental observatories, and even to the amount of 

 from 5" to 10" in those of Greenwich." Indeed, Trough ton 

 has been heard to affirm that a well divided circle of a sin- 

 gle foot in diameter is more to be depended upon than a 

 fixed quadrant of the largest construction. In a series of 

 four observations made with the six inch circles of Kater 

 as constructed by Robinson, I have never found, under 

 favourable circumstances, the errors to exceed ten or fifteen 

 seconds. Now, in the preface to the first volume of the 

 Greenwich observations, published by Maskelyne in 1776, 

 he makes the following remarks : " The sun and moon and 

 some of the principal fixed stars are constantly observed on 

 the meridian every day when the weather will permit ; and 

 the exactness of the instruments is so great, and their recti- 

 fications so nice, that the place of any heavenly body may 

 always be found by them within ten seconds of a degree 

 both in longitude and latitude, and generally much nearer." 

 He then possessed a great mural quadrant of eight feet 

 radius, by Bird, and we, therefore, see that our small cir- 

 cles of a few inches in diameter are nearly as accurate as 

 the old quadrants of as many feet, and they approach much 

 nearer to perfection than we had any reason to anticipate. 

 Such small portable circles are consequently very valuable 

 to the amateur astronomer, as well as the scientific traveller, 

 since in the hands of a skilful observer, they furnish results 

 highly useful for the improvement of geography, astro- 

 nomy, and navigation, while at the same time their mode- 

 rate price enables many to become purchasers. 



In a letter from Captain Kater of the 25th of February, 

 1831, he remarks: *'the size I recommend, and which I 

 use is only 3 inches in diameter, and in the latest con- 

 struction has only a vertical circle which can, however, be 

 placed in the plane of any two objects so as to take the 

 angle between them, the whole contained in a box 7 inches 



