APPENDIX.] NOTE TO CHAP. I. 865 



with perfect accuracy. The use of parallel rulers is not to be 

 recommended. The T square, triangle and drawing-board are 

 far preferable. It should be remembered, finally, that careful 

 habits of manipulation, while -they give constantly increased 

 skill and more accurate results, affect in no degree the rapidity 

 and ease with which those results are obtained. 



