LONGITUDE, 



139 



After giving what I considereil a fair trial in the field to all the methods now known, it was 



concluded to place the chief reliance on tlie transit of the moon. il\ hinvcvcr, it happens to 



me to he again in charge of extensive operations of the kind, I shall make some effort to 



improve the instruments for the ohservation of lunar distances. I am satisfied it is in tliat 



direction itinerant ohservers must look for improved methods and facilitiea in obtaining lonj^i- 

 tude. 



When the reflecting instruments are made so as to he jdaced more firmly and quickly in 

 any given plane, and the methods of computing lunar distances are improved and simi)Iificd, 

 it will be in the power of the observer any clear night, when the moon is above the horizon, to 

 multiply his observations so as to obtain close results. The instruments in present use have not 

 sufficient power to observe near contacts of the moon and stars ; and in the attempts which 

 lave been made to increase the power of the telescope, the instrument becomes insupportable 

 by the hand for repeated or nice observations. 



In all cases where it was not necessary to declare the result on the spot, as at those stations 

 at the extremities of azimuth lines^ and at stations such as the 111th meridian of longitude, 



1 



which formed turning-points in the boundary, the longitude was deduced from corresponding 

 observations made at Greenwich. In some few cases we obtained corresponding observations at 

 the American observatories j but the observations were not sufficiently continuous at any of 

 these last-named observatories to enable us to rely upon them. And I have here to repeat (what 

 I have heretofore expressed to the American Association for the Advancement of Science) my 

 obligations to Astronomer Royal Airy for the trouble he has taken to furnish the corresponding 

 observations in MSS. before they were published at Greenwich. 



In the personal account, mention is made of the agreement made with the Mexican commis- 

 sioner to declare the 111th meridian, from computations based on the data afforded hy the 

 Greenwich Ephemeris,* before receiving the corresponding observations. This arrangement 

 was a necessity arising from our isolated position near the centre of the continent, cut off 

 from all intercourse except by expresses protected by armed escorts. To have awaited the 



-J 



reception of the corresponding observations would have detained us fully eighteen months^ 



at great expense — a result not contemplated bj either the United States or Mexican governments, 

 and not contemplated by the treaty, which provided against any possible errors in the location 



of the line by declaring, 'Hhat line shall alone be established upon which the commissioners 

 may fix; their consent in this particular being considered decisive and an integral part of this 

 treaty, without necessity of ulterior ratification or approval, and without room for interpreta- 

 tion of any kind by either of the parties contracting 



a* 



17 



Whippl 



5, 10, and 16, by Assistant John H. Clark ; at 18, by Assistants Gardner and Clark ; and at 12, 

 by Lieutenant W. F. Smith. At most of the stations the observations were carried through at 

 least three lunations ; but, it will be seen, the result was not changed materially after the 



first lunation. 



The longitude of the point where the boundary leaves the Eio Bravo was transferred from 

 Frontera by triangulation ; and the longitude of El Paso and of No. U (the caHon) were resjiect- 

 ively transferred from Frontera and San Elceario by flashes of gunpowder simultaneously 



American Ephemeris had been rectived, nor -was I aif»re 



published. 



