158 



AMERICAN FORESTRY 



WOOD FOR THERMOMETER BACKS 



The glass tube of a thermometer will be broken i{ fastened to a wood that warps, so the better grade of thermometers have backs 

 of walnut, cherry or mahogany, as they show little tendency to warp. These logs are black walnut. 



India, Australia and the Philippines pass as mahogany, 

 without too close insistence on botanical distinctions. 

 Mahogany is little disposed to warp, shrink, or swell, 

 and that characteristic makes it of special value for in-*~ 

 struments which must retain their shapes under climatic 

 changes. The makers of cameras employ a large quan- 

 tity of mahogany, and it is liked for T-squares, and for 

 numerous other small articles. 



The uses of cocobola, lignum-vitae, teak and ebony are 

 less extensive, and although these foreign woods are 

 serviceable and handsome they cannot be considered very 

 important in this industry because not used in large quan- 

 tities. 



The T-square is so called from its shape. It is used 

 by draftsmen and mechanics in establishing perpendicu- 

 lars. In making this instrument, a wood is wanted which 

 is not liable to warp, and the best are mahogany and 

 walnut, though a number of other hard and dense woods 

 are employed. This square is often of large size, and it 

 cannot well be made of steel because that metal is too 

 heavy. Wood holds first place. 



A large bill of lumber goes into thermometers ; but 

 most of these are of ordinary woods, such as yellow pop- 



lar, basswood, tupelo and pine. Thermometers may be 

 only a few inches long, or they may be three or four 

 feet, and in the aggregate they call for a rather large 

 amount of wood. 



By some unwritten law or widely respected custom, 

 the spirit level is supposed to be made of cherry, though 

 many are not, some being mahogany, walnut and other 

 woods that hold their shape well after having been sea- 

 soned. It is a tool employed by builders in plumbing 

 walls and leveling foundations and sills. Wood is rated 

 superior to metal for large spirit levels because weight 

 must be held within reasonable limits. Other advantages 

 are claimed for wood, the chief of them being that this 

 material is almost entirely free from tendency to become 

 distorted under the influence of heat and cold. 



Wood's superiority to other available materials for 

 cameras is unquestioned. Its light weight alone gives it 

 an advantage. The wooden portion of the camera is a 

 box which contains the plates or films and the lenses. 



Several woods serve for tripods for cameras, kodaks, 

 and surveying instruments. Among the best are birch, 

 maple, walnut, mahogany, rosewood and ebony. 



