244 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



divided into two sections one on the North Atlantic, and 

 the other the South. This volume is a fit accompaniment 

 to one previously noted, constituting a coast pilot to a por- 

 tion of the shores of Brazil. No. 45, Hep. of Hydrographic 

 Office. 



LONGITUDES OF WASHINGTON AND GREENWICH. 



On the recent occasion of the determination of the longi- 

 tude between Washington and Greenwich it was found con- 

 venient to employ an intermediate point located on the French 

 coast, and the opportunity was improved by Mr. Hilgard, of 

 the Coast Survey, to make a new determination of the differ- 

 ence in longitude between Paris and Greenwich. The inter- 

 est which attaches to a determination between the two old- 

 est observatories of Europe by the astronomers of the New 

 World increases when we learn that the result of this latest 

 determination of longitude varies very little from that made 

 by the European astronomers in 1863, but differs widely from 

 that which has hitherto been adopted as the correct longi- 

 tude. Proc. Amer. Assoc, N~. Y. Trib., October 31, 1873. 



LONGITUDES AT SEA. 



The accuracy of the determination of longitude at sea by 

 the employment of chronometers forms the subject of an in- 

 teresting communication from De Magnac^-a subject that 

 has also attracted much attention in connection with the loss 

 of several valuable vessels with precious human freight. De 

 Magnac states that of all the physical causes acting at sea 

 upon the chronometers, the principal are the atmosphere and 

 the time. The construction of chronometers has been carried 

 to so high a degree of perfection that the function which rep- 

 resents the daily rate of the chronometer is almost always 

 a continuous function of the above-mentioned data; but it is 

 still' uncertain whether we can rely upon absolute immunity 

 from some sudden change in the rate of any one chronometer. 

 Therefore it would be highly unsafe to rely in a long voyage 

 upon an isolated chronometer; and neither can we study the 

 action of the disturbing causes unless several of these instru- 

 ments are carried upon the same vessel. The author has, 

 therefore, during the years 1871-73, observed with accuracy 

 all the chronometers upon the vessel Jean Bart in its voy- 



