DEPARTMENT OF TERRESTRIAL MAGNETISM. 261 



bow method. Fibers of a diameter less than 0.002 mm. are more readily 

 obtained by the flame method as described in detail by Coblenz.^ 



Following the general method due to Boys,^ various kinds of woods were 

 tried out for bows. Bows were made up in different cross-sections and 

 lengths; an improved type of trigger release and bow holder was evolved, 

 and materials for arrows were investigated. Ash, lancewood, greenheart, 

 and long-leaf pine were tried for bows, while soda straws, wheat straws, and 

 slivers of wood were tried for arrows. 



A satisfactory target was constructed of two squares of corrugated card- 

 board with an air-space of 1 inch between them and hung about 3 inches from 

 a vertical wall. It was found that the arrows would embed themselves about 

 half their length in the two pieces of corrugated board without in any way 

 damaging the arrows. 



The collecting of fibers after shooting was facilitated considerably by the 

 use of four light wooden stands about 3.5 to 4 feet high, carrying lengths of 

 glass tubing parallel to the floor. They were placed so as to divide the 

 space of 30 feet between the bow and the target into five equal parts. The 

 fibers shot were found to rest on the row of parallel glass rods, and it then 

 became an easy matter to mount them on small wooden frames or otherwise 

 store them. The diameters of the fibers are readily measured with a high- 

 power microscope equipped with graduated eye-piece. 



A most useful accessory for fiber work was a small electric heater operating 

 from a storage battery or small alternating-current transformer. It con- 

 sisted of a Cutler-Hammer 70-50 switch into one end of which was set a 

 short length of bakelite rod. Two brass wires were set into grooves in the 

 bakelite rod and a loop of resistance wire mounted in the outer ends. This 

 loop was bent in the form of a small hairpin and glowed to redness when the 

 proper current was sent through the loop. The Cutler-Hammer switch 

 enabled the heater to be turned on and off by the hand holding it. This 

 heater was found convenient not only for attaching short lengths of fibers 

 to suspension hooks and for dropping bits of molten shellac as little anchors on 

 to the fibers when collecting and storing them, but also proved its usefulness 

 in many other ways. 



The fineness of a quartz fiber obtained by the cross-bow method depends 

 to some extent upon the elastic properties of the bow and the velocity with 

 which the bow returns to its position of equilibrium after the trigger is 

 released, but mainly upon the size of the piece of quartz fused. Slivers 

 of clear quartz about one thirty-second inch or 0.5 mm. in diameter, heated 

 to a dazzling whiteness in an oxyhydrogen flame, for about one-eighth inch 

 of the sliver, gave the finest fibers. Fibers made from cloudy quartz rod or 

 from quartz heated in an oxyacetylene flame proved unsatisfactory. With 

 a bow of given elasticity and an arrow of minimum mass, the smaller and 

 hotter the bit of quartz heated, the finer the fiber drawn out. From hundreds 

 of shots made with this apparatus, it is concluded that the secret of obtaining 

 long, fine quartz fibers of uniform cross-section resides in the amount of quartz 

 heated and the temperature to which it is raised. 



Report on determination of geographic positions and magnetic elements at Maya ruins, 

 Peten, Guatemala, 1923. W. A. Love. 



The Department cooperated with the party sent out by Dr. S. G. Morley, 

 Associate of the Institution in Middle-American Archaeology, under the 



' See "Investigation of infra-red spectra," by William W. Cobleatz, Carnegie Inst. Wash. 

 Pub. No. 65, 126-127 (1906). 



2 See R. Threlfall's "On laboratory arts," Macmillan & Co., 1898 (196-226). and "On the 

 elastic constants of quartz threads," Phil. Mag. (July 1S90). 



