MATHEMATICAL INSTRUMENTS. 43 



Fi s .G3. Fig. 66. Fig. 67. Fig. 68. 



Centrolinead. (Fig. 74, page 45.) The Centrolinead is an 

 instrument used in perspective drawing, for drawing lines to- 

 wards a distant centre, as towards a distant vanishing point. 

 They are made in pairs right and left. In the cut, the blades 

 are represented as broken off. Price, with blades, each $10. 



Improved Circular Protractor. (Fig. 75, page 45.) 

 This instrument consists of an entire circle, A A, connected 



