112 



TJ. S. COAST AND GEODETIC SURVEY. 



meridian and upon the parallel in the vicinity of the prin- 

 cipal place of the country the map of which he wished to 

 construct. One part of the condition is fulfilled by making 

 the meridian of the place become the central or straight 

 hne meridian, for in that case the derivative of l with 



respect to X becomes zero for X = 0. We can now equate 

 to zero the first derivative of Tc with respect to p upon this 

 meridian; it would merely be necessary to consider <pm as 

 the latitude of the given place. The second derivative will 

 also become equal to zero if we take 



