In going to Lan-chou Fu from Yen-an Fu the Longitudes of Ch'ing- 

 yang Fu and Ku-yiian Chou were not satisfactory, as Grant only had two 

 watches and the time consumed was too great. In coming back he took 

 a second set, which worked out exceptionally well, the rates of the 

 watches having been very regular, and the time consumed by the journey 

 being comparatively short. The Longitude of Yen-aft Fu, as determined 

 by the watches, was i09°-27'-33", and that as calculated from occultation 

 previously taken i09°-26'-49". However; calculating the Longitudes back 

 from Yen-an Fu, as a starting point, the biggest variation was 2'. We 

 consider the chronometer Longitudes correct to i mile. 



The position of Lan-chou Fu (South Gate) was fixed as Lat. 

 36°-3'-6"; Long. i03°-40^-54". This was the only place on our trip where 

 we had a subsequent opportunity of comparing our determinations with 

 those of another traveller. Mr. Clementi, who travelled from Kashgar 

 to Kowloon in 1907-8, gives the position of Lan-chou Fu as Lat. 

 36°-3'-ii"; Long. i03°-46'-7". His latitudes were taken by N. and S. 

 stars and his longitudes by chronometric differences. 



Altitudes. 



After leaving T'ai-yiian Fu all determinations to within 30 miles of 

 the Yellow River were trigonometrical {i.e., obtained by vertical angles 

 with a theodolite). All subsequent heights are barometric. For baro- 

 metric determinations they can be taken as reasonably accurate, as the 

 aneroids were frequently compared with the mercurial barometer. The 

 mean of the barometer and the boiling-point readings was taken as the 

 correct height. 



Previous Surveys. 



Without pretending to give any exhaustive record of previous foreign 

 surveys of the country traversed, we offer a slight summary of such as we 

 have been able to trace. 



Early in the Eighteenth Century the Emperor Kang-hsi ordered 

 a survey of the Eighteen Provinces to be carried out. In this he 

 most probably had the assistance of the Jesuit Fathers, whose influence 

 during this reign was very great. The Chinese method of map-making 

 is to give a separate sheet for each ** Fu " or " Hsien " district, and it 

 is of course possible to piece together a number of these sheets to form 

 a survey of the whole country. This however leads to a thoroughly 

 untrustworthy map, as it is vital ** to work from the whole to the part, 



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