Mr Bufelianan's Deicnption and Uses of Piotractiug Table. 141 



construction of a similar table for him, this has now been ac- 

 complished in a very superior style, having been commenced, 

 and the principal parts formed, by the late Mr Dunn, optician 

 here ; the frame-work and other parts of the table by Mr 

 Sandeman, cabinet-maker; and the whole completed by Messrs 

 Adie and Son, opticians, and with a degree of accuracy and 

 perfect workmanship which is highly satisfactory. 



The principle of this machine consists in having the sheet 

 or table on which the survey is to be laid down moveable 

 round a centre, whereby it can be set to any required angle ; 

 while the straight edge or ruler for drawing or laying down 

 these angles remains in a fixed position as to the angles, but 

 capable of having a parallel motion across or throughout the 

 sheet. Hence the instrument consists of three essential 

 parts. 1*/, The circular table or drawing-board on which the 

 sheets for laying down the surveys are fixed. 2rf, The pro- 

 tractor or divided circle on which the degrees and minutes^ 

 are accurately marked ; and, Sr/, The parallel ruler and straight 

 edge by which the angles are drawn to any degree or minute, 

 and from any point throughout the sheet on which these angles 

 may have been taken during the survey. The whole apparatus 

 of table, protractor, and parallel ruler, are set on a frame which 

 can be elevated to any angle for the convenience of working* 

 See perspective view. 



The board or table consists of a strong mahogany framed 

 circular drawing board, 3 feet 1 inch in diameter, |tks of 

 an inch thick, calculated to receive a sheet of the common 

 atlas drawing paper 33 inches by 26, w^hich being fixed down 

 along the edges by paste or gum, is stretched out to a smooth 

 and even surface. 



The protracting circle extends round the circumference of 

 tlie drawing board, and the great advantage of this arrange- 

 ment is, that the degrees and minutes are forme<l on so large 

 a scale that they can be readily distinguished by the eye, and 

 laid oft^" with the greatest expedition as well as accuracy. In 

 the original instrument, this circle was formed by a circular 

 plate of brass laid along the circumference of the drawing 

 board ; but in the present instrument, Mr Dunn has introduced 

 an entire circle or wheel of braids extending from the centre 



