242 /. Locke on the Electro-Chronograph. 



It is, therefore, well entitled to be called a most important dis- 

 covery. It is a national triumph, and it belongs to that class of 

 achievements by which the most beautiful and enduring monu- 

 ments are erected to national honor and greatness ; and my feel- 

 ings of professional pride will not allow me to pass it by, without 

 calling your attention to the garland that has been hung about it 



by the navy. 



To the navy belongs the honor of having first applied the mag- 

 netic telegraph to the determination of longitude. Five or six 

 years ago Capt. Wilkes, of the navy, used it for determining the 

 difference of longitude between this city and Baltimore. This 

 was the first time it had been applied to such a purpose, and it 

 was a great improvement upon the methods which up to that 

 time had been used for finding the longitude, for it reduced the 

 results down to the accuracy with which the time between the 

 ticks of the second-hand could be measured on the face of the 

 clock by the eye and the ear. And thus the honor of being the 

 first to convert the magnetic telegraph into an astronomical instru- 

 ment, and that too into one of great practical value and impor- 

 tance, was secured by one of its officers to the American navy. 

 Though the errors of the problem were greatly reduced by this 

 discovery, there were, however, small sources of error still remain- 

 ing, and it remained for Dr. Locke, formerly an officer of the 

 navy also, to devise a means of eliminating them so completed 

 that now there is scarce a trace left in the results, so free are they 

 from doubt and uncertainty. The probable error of longitude 

 determined with Dr. Locke's clock is brought within such narrow 

 limits that if, while the astronomer in St. Louis or elsewhere were 

 operating upon the magnetic clock here for his longitude, the ob- 

 server in Washington were to move from one instrument to another 

 in this building, the fact that he had moved would be made known 

 at once, and whether he had moved to the east or the west would 

 be told by the clock, and appear in the resulting longitude. 



Dr. Locke was formerly a member of the medical corps of 

 the navy, and as such, spent a portion of his manhood and prime 

 years of his life at sea. 



It is therefore, not surprising that sailors should be quick to 

 lay hold of the problem of longitude through any improved 

 means that may be offered for its solution. Every one can see 

 the importance of accurate determination of longitude, but sailors 

 both see and feel it. In his letter to me, describing his clock and 

 giving an account of its performance, Dr. Locke kindly offers to 

 put one in this Observatory. 



It would be of incalculable service and advantage. It would 

 increase the accuracy of results, and greatly multiply them in 

 numbers. With this clock one observer could do more and better 

 work than two can now. An illustration of the value of such a 



