BRITISH CONTRIBUTION 143 



Harrison was eventually awarded the prize offered by Parlia- 

 ment to *'such person or persons as shall discover the Longi- 

 tude" in 1772, and a copy of his successful chronometer was 

 used by Capt. Cook on his second and third voyages, giving 

 extremely accurate results. This method by 'transport of 

 chronometers' finally superseded that by lunar distances. 



Though these instruments were initially used in navigation 

 and hydrographic survey, it must be remembered that the 

 explorers of the following century relied largely upon the 

 sextant (an improvement on the quadrant) and the chrono- 

 meter for the surveys they were able to accomplish. Another 

 survey instrument which at this time emerged in its essentials 

 was the theodolite, a descendant of the 'polymetrum' devised 

 in the early sixteenth century. By the invention in 1763 

 of his graduating engine, Jesse Ramsden solved the problem 

 of dividing the brass circle accurately, and then worked 

 on his famous theodolite for a number of years. This 

 included a horizontal circle three feet in diameter, which 

 by the aid of micrometers enabled readings to single seconds 

 to be obtained. The sighting vane of the older models was 

 replaced by a telescope moving freely in the vertical plane of 

 the instrument. This theodolite was admittedly heavy and 

 cumbrous, but it proved the most efficient instrument for 

 observing angles in survey, and by gradual modifications it 

 has developed into the highly precise and portable patterns 

 of today. This instrument was first employed in the connexion 

 by triangulation of England and France in 1787, and later 

 in the Ordnance Survey of Britain and in India. 



The first results of these technical advances were seen in 

 the increased accuracy of hydrographic charts, and in their 

 production and publication Great Britain assumed the lead 

 which she has maintained for the last 150 years. The end of the 

 eighteenth century may be approximately taken as the point at 

 which the general outline of the continents, outside the Polar 

 circles, and their precise position had finally been determined, 

 though much patient and careful work had still to be carried 

 out before all the details were filled in. In the remainder of this 

 outline, therefore, we shall no longer be concerned with the 

 seaman's contribution to the/unroUing of the map', but must 



