542 



NATURE 



[October i, 1908 



SURVEYING FOR ARCH.^OLOGISTS.' 



IV. 



Simple Tnstnimoils for Measuring both Magnetic 



Azimntli and Altitude. 



ALTHOUGH undoubtedly for final observations at 

 any monument a theodolite must be employed, 

 using the sun or a star in order to obtain astronomical 



inometer. 



or true bearings and so avoid all magnetic difficulties, 

 and reversing the telescope to secure the correct alti- 

 tude of the horizon ; for rapid sur- 

 veys there are many handy forms 

 of instrument by means of which 

 preliminary information can be 

 gathered, both with regard to 

 azimuth and, what is equally im- 

 portant, the angular height of the 

 horizon. 



It is quite certain that the use of 

 the prismatic compass, in spite of 

 its great convenience, must give 

 way to other instruments which 

 enable us to determine approxi- 

 mately the altitude of the horizon 

 as well as the azimuth of any object 

 the bearing of which we wish to 

 obtain. 



As a matter of fact there are now 

 several such instruments available. 

 They consist in the main of an 

 azimuth compass, with an addition 

 generally called a clinometer, 

 enabling angles to be measured in 

 a vertical plane. For this addition 

 Ihe first requisite, of course, is to 

 be able to determine the true hori- 

 zontal plane at the place of observa- 

 tion. This can be done by using 

 a water level, a pendulum, or a properlv adjusted 

 •bubble. I will give a brief description of three 



^ Cjntinued from p. 511. 

 NO. 2031, VOL. 78I 



instruments which are based upon these various 

 methods. 



For the angular measurement of elevation, includ- 

 ing, therefore, the angular height of the horizon as 

 seen from any monument, the archaeologist may use 

 a very simple and convenient addition to the compass 

 devised by .M. Hue, a distinguished French archa-olo- 

 gist. He uses the water-level principle. The method 

 employed can be readily gathered from the accom- 

 panying woodcuts, obligingly sent to me by the pub- 

 lishers of, the "Manual of Prehistoric Researches," 

 published by the Societe prehistorique de France ; a 

 book which shows us, by the way, that the French 

 archaeologists are much more thorough and philo- 

 sophical in their inquiries than their British brethren. 

 It is not a question of the spade versiis the theodolite, 

 but of the spade and the theodolite, and as full in- 

 structions are given about one as about the other. 



It is quite refreshing to read the chapter " Indica- 

 tions pour faire un lev^ de Terrain a la Boussole," 

 and then the instructions given relating to subsequent 

 work with the large-scale maps published by the 

 French Government. 



In Barker's instrument, called for short a clino- 

 ccmpass, we find the pendulum method employed. 

 The altitude zero of the instrument is shown when 

 the pendulum hangs vertically at rest. This is an 

 addition to the azimuth compass, and can be used 

 when the azimuth measures have been made by 

 making the plane of the instrument vertical. The 

 figure will show the method of use. The degrees of 

 elevation can be read under the prism as well as by 

 the pointer at the bottom. 



In a reconnaissance lately among the .\berdeen 

 circles I employed a clino-compass of Barker's pat- 

 tern; it weighs only a few ounces and is carried in a 

 sling over the shoulders; even a tripod can be dis- 

 pensed with, though it is much better to have one; 

 the lightest form is that supplied by the Kodak Com- 

 panv for their cameras, to which must be added an 

 adapter at the top to fit the base and allow the instru- 

 ment to be used horizontally and vertically. In this 

 form, especiallv in the case of the altitudes, the mean 



Fig. 15. — Vertical readings with Barker's clino-compass. An elevation of 3Mndicated. 



of several observations should be taken. In my 

 opinion, a desideratum for such work is a simple small 

 instrument with level and reversible telescope lor small 



