Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. In the opening chapter, the construction of scales naturally leads to a discussion of the principles upon which the construction of various slide rules is based. The second Chapter develops the principles of a network of scales, showing their application to the use of various kinds Of Coordinate paper and to the charting of equations in three variables.