Chemical and Physical Papers. 53 



feet long and six inches wide. Looking on the outer edge of the 

 blade we find 12; between the fifth and sixth lines under 12 will 

 be found 12 again. This is the length of the board. Now follow 

 the space along towards the tongue till we come to the cross-line 

 under 6 (on the edge of the blade), this being the width of the 

 board ; in the space will be found the figure 6 again, which is the 

 answer in board measure, namely, six feet. 



On some squares will be found on one side of the blade nine 

 lines, and crossing these lines diagonally to the right are rows of 

 figures, as seven I's, seven 2's, seven 3's, etc. This is another style 

 of board measure, and gives the feet in a board according to its 

 length and width. 



In the center of the tongue will generally be found two parallel 

 lines, half an inch apart, with figures between them ; this is termed 

 the brace rule. Near the extreme end of the tongue will be found 

 24-24, and to the right of these 33-95. The 24-24 indicates the 

 two sides of a right-angle triangle, while the length of the brace is 

 indicated by 33-95. This will explain the use of any of the figures 

 in the brace rule. On the opposite side of the tongue from the 

 brace rule will generally be found the octagon scale, situated be- 

 tween the central parallel lines. This space is divided into inter- 

 vals and numbered thus : 10, 20, 30, 40, 50, 60. Suppose it becomes 

 necessary to describe an octagon ten inches square : draw a square 

 ten inches each way and bisect the square with a horizontal and 

 perpendicular center line. To find the length of the octagon line, 

 place one point of the compasses on any of the main divisions of 

 the scale and the other leg or point on the tenth subdivision. This 

 length being measured off on each side of center lines, touching 

 the line of the octagon, will give the points from which to draw 

 the octagonal lines. The size of the octagon must equal the num- 

 ber of places taken off from the tongue by the compasses. 



We shall now proceed to lay off the lengths, cuts and bevels for 

 the timber in a hip roof 24 feet wide by 32 feet long, the hips to 

 be at right angles and the roof to have a pitch of 45 degrees, leav- 

 ing a ridge of 8 feet, the distance from the plate to the center of 

 the roof being 12 feet, and the rise of the roof being the same, 

 measure with the rule diagonally across from tongue to blade 

 on the outside edge having the twelfth scale from 12 to 12. The 

 distance on the rule will be 17 inches, or feet, the length of 

 common rafter, and the figures 12 by 12 will mark the heel or seat 

 cut, and also the plumb cut against the ridge board. It will be 

 noticed that every foot gains five inches on the diagonal. Next 



