PRESIDENTIAL ADDRESS. 423 



figures, it would be easy for quite useful plans to be constructed, as indeed we 

 know was the case. 



The longer distances were reckoned by the time it took to travel from one 

 place to another, days' journeye, &c. ; and later on in stadia, of which it is 

 generally assumed that there were 600 to a degree according to the ordinary 

 Greek measure. 



When distinctive "features were visible it would be comparatively easy to 

 map roughly a route travelled, much as a man in the present day can make an 

 approximate sketch to show any journey he has taken, even without a compass 

 or other instruments ; or natives have been able to draw rough sketches to 

 explain to explorers the direction of any coast line, or course of a river. One of 

 the most recent examples of this is the map reproduced by Mr. Beaver, which 

 was drawn in the sand by a native of Papua to show the relative position and 

 names of the various tributaries of a river he was exploring (see ' Geogr. 

 Journal,' April 1914). 



Long before the magnetic compass was known, at any rate in Europe, navi- 

 gators and travellers had to find their way somehow, often through little-known 

 regions, and, when they had no landmarks to direct them, would have to seek 

 some other means of guidance. Early nomad peoples of the desert would soon 

 become acquainted with the heavenly bodies and their general movements and 

 positions, and would naturally turn to them for the guidance they sought. 

 Their positions at certain times and seasons would, through being continually 

 observed, become quite familiar, and so doubtless before any instrumental 

 astronomical observations for fixing positions were made, men learned to march 

 and steer their ships by the sun by day and the stars by night. It is interesting 

 to note that the art of marching by stars has been considerably revived in the 

 last few years, specially in the rapid movement of troops at night. 



So long ago as the seventh century B.C., Thales bad taught the Ionian sailors 

 to steer by the Little Bear, as did the Phoenicians. 



One of the most interesting exploring expeditions of ancient times was that 

 of Pytheas, the discoverer of Britain, in the third century B.C., who had not 

 only learnt to sail by the stars, but determine the latitudes of points throughout 

 his voyage by astronomical observations, made with a gnomon or sort of sun- 

 dial, with which he seenie to have fixed the latitude of Marseilles with far 

 greater accuracy than might have been expected. 



The gnomon used by Pytheas was probably of the earlier form, which con- 

 sisted merely of an upright rod in the centre of a flat disc, but Aristarchus, in 

 the third century B.C., introduced a decided improvement in the design of this 

 interesting old instrument, which deserves to be borne in mind by all surveyors, 

 since it seems to have been the first by which angles could be measured directly 

 without computation. He substituted for the flat disc, or plate, a hemispherical 

 bowl, in the centre of which an upright rod was fixed equal in length to the 

 radius of the bowl. Concentric equidistant semi-circles were drawn on the 

 interior of the bowl, which became a scale for the direct measurement of angles 

 of altitude as indicated by the shadow of the rod or gnomon. 



The voyage of Pytheas is of special importance, since it shows that even at 

 that early date serious attempts were made at carrying out geographical exploring 

 expeditions, by sea at any rate, on scientific lines. 



The first record of anything that could be con.'sidered as the beginning ot 

 geodetic surveying was the well-known attempt of Eratosthenes to ascertain the 

 size of the earth by the measurement of an arc of the meridian. This wonderful 

 old philosopher was born in Cyrene in B.C. 276, and was so noted for his learning 

 that he was put in charge of the famous library at Alexandria. The method 

 he adopted was much the same in principle as that upon which geodesists at 

 the present time work, but it seems impossible to say how near the truth his 

 results were, as there is a doubt as to the length of the stadium he used. 



The subject of the true form and dimensions of the earth is a most important 

 one in many respects, and considerably affects survey questions, since it must 

 form the basis of aU exact measurements on the earth's surface. Right on to 

 the present day geodesists have been working at it, and although they have 

 brought down the probable error in the measurements to a minimum, yet even 

 now the question cannot be takep 3s finally settled. 



