432 PIONEERS OF SCIENCE IN AMERICA. 



Such signals are, of course, subject to the errors that always 

 attend the action of human nerves and muscles, so the next 

 problem was to make the clock give its own signals. Two 

 methods had been proposed, but there were fears groundless 

 they have since been proved that either of these would in- 

 juriously affect the running of the clock. Mr. Walker sought 

 diligently for some apparatus that would not arouse any such 

 fears. He propounded the problem to several astronomers, 

 and two or three contrivances were devised for the pur- 

 pose. 



This mode of observation and the apparatus invented to 

 meet its requirements proved valuable not alone for determi- 

 nations of longitude, but also for all other astronomical obser- 

 vations requiring minute precision in the determination of time. 

 The mental effort required of the observer being reduced to a 

 minimum, many more transits could be observed at a single 

 meridian passage. Walker immediately modified the transit 

 instrument to suit the new requirements, and, instead of five, 

 seven, or at most nine threads, he provided it with several 

 tallies of five threads each. There remained but one requisite 

 to complete the American method of observation. This was 

 some mechanical contrivance for securing a uniform rotary mo- 

 tion of the record sheet. It had not been attained when Walker 

 died, although some progress toward the solution of the prob- 

 lem had been made. 



It is proper for the biographer to point out the share which 

 Walker personally had in this series of inventions, although he 

 was far from making any such claims for himself. With a fine 

 comradeship he was jealous only for the credit of the organi- 

 zation of which he was a member -the United States Coast Sur- 

 vey. Speaking to the American Association for the Advance- 

 ment of Science, Walker said : " With the single exception of the 

 experiment between Baltimore and Washington, in 1844, 1 know 

 of no telegraphic operation for longitude, and of no step in 

 the improvement or perfectionment of the art, in Europe or 

 America, which has not been the work of the officers proper of 

 the Coast Survey, or of commissioned officers and civilians 

 acting temporarily as assistants. ... I will not here allude 

 to the respective claims of Americans for priority or superior 

 excellence of inventions and suggestions, believing that it will 

 be becoming for all of us to look to the great work that has been 



