436 Forestry Quarterly 



New Abney Level and Its Use 



The improved Abney level, as illustrated in Fig. 1, is only 

 slightly larger than the old Abney, and its cost is about the same. 

 The arc is made larger and graduated to read directly the difference 

 in elevation per chain (66 feet) of horizontal distance; a prism has 

 been substituted for the German silver reflector; the bubble tube 

 is made longer and with adjustment devices similar to those on 

 the bubble tube of a transit. Also the bubble tube support is 

 attached rigidly to the indicator arm of the arc, thus eliminating 

 the inevitable loet motion between these two parts existing in all 

 old-style Abneys. The bubble tube is arranged to allow adjust- 

 ment to eliminate refraction, which made the old-style instru- 

 ments so unreliable in measuring steep slopes. A semi-circular 

 lens placed in the fore end of the eye-piece tube, as in the Locke 

 level, magnifies the movement of the bubble so as to greatly 

 facilitate accurate sighting. The various changes introduced 

 have so improved the instrtmient and the results of its intelligent 

 operation have proved so surprising, that the new Abney will 

 doubtless meet with favor among the entire engineering profession, 

 and its scope of use in field work of all kinds greatly extended. 



Aside from the special graduation shown in Fig. 1, which is 

 applicable to all topographic work, plates with the usual degree 

 and per cent graduations are furnished and also a special gradua- 

 tion to give directly horizontal distance from slope chaining. 

 This graduation has foimd much popidarity in cadastral surveys. 



Topographic Surveys of Timber Lands 



There was some objection at first to the Abney method on 

 accoimt of the necessity of taping the slope distances, but two 

 years of use have proved that this work can be done with practi- 

 cally the same convenience and time as pacing. 



The unit of meastirement adopted was the chain of 66 feet for 

 the reason that a large portion of the work is the retracement of 

 land survey lines recorded in that imit, and also for convenience 

 in timber estimating. Obviously a definite horizontal unit is 

 necessary for operation without the use of tables, and after thorough 

 trial it was found that a distance of 2 chains was the most con- 

 venient for rough country covered with heavy timber. A special 

 2V2-chain tape has therefore been designed for use with the 

 Abney method, the tape proper consisting of 2-chaiti lengths 



