176 THE POPULAR SCIENCE MONTHLY. 



death. The watches of railway employes are usually set by one 

 clock, but a difference of one or two minutes on a crowded road may 

 briuo- about the most fatal results, as the reports of the various rail- 

 way commissions will show. If a ship leaves New York supposing 

 her chronometer which is regulated to Greenwich time to be losing 

 two seconds a day, while it is really losing six, every day she is really 

 about a mile farther west than her reckoning shows her to be, and in 

 a voyage of a month she will suppose herself to be too far west by 

 thirty miles. Such a result may be attended with the most disastrous 

 consequences, and that it does not oftener so result is due to the skill 

 and watchfulness of sea-captains, a class of men whose vigilance and 

 faithfulness are too little appreciated. 



That such accidents do occur is brought constantly before us, in 

 the reports of marine disasters as given in the newspapers and else- 

 where, and every year a large volume is published by the English 

 Government the "Report of Wrecks and Casualties," etc, in which 

 the details are given. A simple inspection of the wreck-chart appended 

 to this bulky annual volume, where every vessel wrecked during the 

 year has the place of her loss indicated by a dot on the map, shows 

 how frequent such losses are. I know of no simpler way of presenting 

 the risks run, when the actual wreck is not incun-ed, than by giving the 

 following table from the report for 1863 of Mr. Hartnup, Director of 

 the Observatory of Liverpool, an observatory founded especially for 

 the care of the chronometers of merchant-ships. 



The work of this observatory has been continued for many years, 

 and a large mass of statistics concerning the running of the chro- 

 nometers of ships sailing out of Liverpool has been accumxxlated and 

 partially discussed. 



In the earlier history of the observatory, its attention was confined 

 to the rating of chronometers, and, when any chronometer was sent 

 to a ship with a given correction and rate^ a record was kept of the 

 fact. 



On the return of the chronometer to Liverpool every effort was 

 made to find the correction and rate which were given at the foreign 

 port to which the ship was bound, and in this way a vast amount of 

 statistical information concerninof the runninsr of the chronometers of 

 merchant-ships out of Liverpool was accumulated. 



In tbe following table, which summarizes these statistics, the^r^^ 

 horizontal column contains the length of the voyage in months ; the 

 second^ the average error of longitude in geographical miles on the 

 equator, deduced from the means of 1,700 chronometers; and the re- 

 maining columns show the average error of the best ten instruments 

 in one hundred, of the second best ten, etc. I have only taken so 

 much of the table as would include a voyage of four months, since a 

 vessel could hardly be without means of correcting her chronometer 

 for a much longer time than this. We may fairly say that this table 



