( 65 ) [HOP 



Hollow-backed.- A board is said to be hollow-backed when a 

 small amount of wood has been removed from the central 

 part of the back side in order to reduce its shipping weight. 



Hollow Chisel Mortising Machines. A mortising machine which 

 cuts a mortise by means of a square hollow chisel. An 

 auger revolves in the centre of the chisel and bores a hole, 

 while the corners are squared out by the chisel as it is fed 

 into the wood. For a long mortise several holes are made 

 one after the other in line. 



Hollow Trunk. Trees decaying in the trunk. Best treated by 

 cleaning out all decaying matter, and when dry painting 

 interior with creosote, then filling up with clean gravel and 

 sand, with a surface coating of cement, adding generally a 

 coat of tar. 



Holly (Ilex Aqmjolium).A- white and hard wood, extremely 

 fine grained. Found all over Europe and Western Asia. 

 Used for engravers' blocks, fancy turnery, etc. It is mainly 

 an ornamental tree. 



Holm Oak (Quercus Ilex) or " Evergreen Oak." An oak known 

 but not common in Britain, the wood of which is strong, 

 hard and heavy. See " Oaks." 



Hook. The angle between the face of a tooth and a line drawn 

 from the extreme point of the tooth perpendicular to the 

 back of a band saw, or to the centre of a circular saw. Hook 

 is stated in terms of inches. On a band saw it is measured 

 between the two lines prolonged to its back ; on a circular 

 saw it is measured along the opposite side of the triangle. 



Hoppus' Measure. A method of measuring the cubical contents 

 of logs and other round timber. In theory it reduces a 

 round log to its square equivalent. 



Hoppus' Measurer, the old standard book of measurement of 

 timber, is one of " customary measure " (ivhich see), except 

 in the instance of square logs, when it is " actual measure" 

 (which see). The method is by string-girth, reducing the 

 length into one fourth, called " quarter girth," and applying 

 thereto the 144 divisor ; whereas in round timber the 

 "actual measure" should be the 113 divisor. See "Cus- 

 toms Measure." 



Hoppus' system of measurement by the 144 divisor gives 

 the correct cubical contents of square timber, but is inac- 

 curate in some of the calculations for unequal sided timber, 

 and for round timber the error amounts to 27 per cent. 



To ascertain the true contents of a cylindrical body by 

 the quarter girth measurement, the divisor employed should 

 be 113 instead of 144. This gives an exactly correct result 



