TRANSACTIONS OF THE SECTIONS. 27 



Account of a recent successful Experiment to determine, hy means of 

 Chronometers, the difference of Longitude between Greenwich and 

 Neio York. By E. J. Dent. 



The rapid transmission of chronometers now practicable by means 

 of steam-vessels from one meridian to another, offers great facilities for 

 the determination of the differences of longitude. This led me (said 

 Mr. Dent) to embark four chronometers on board the British Queen 

 steam-vessel, on her first voyage from England to America. Captain 

 Roberts, the commander of the vessel, kindly undertook the charge of 

 them, and (through the interest of Messrs. E. and G. W. Blunt, of New- 

 York), Jesse Hoyt, Esq., the collector of customs at that port, gave a free 

 permit, as well as every other facility, for landing them. They were then 

 compared daily with two astronomical clocks at the observatory at 

 Brooklyn, 4,700 feet, or 4*09 sec, east of the City Hall, in New York. 

 The errors of these clocks were determined by transit-observations on 

 the days of arrival and departure. The errors of the clock with which 

 the chronometers were compai'ed at Greenwich immediately before the 

 embarkation on board the British Queen, and also immediately after 

 their landing at Greenwich from that vessel on their return, were de- 

 termined by means of several series of zenith-distances of stars on both 

 sides of the meridian, and also of the sun, taken with a sixteen-inch 

 altitude and azimuth instrument at the Royal Naval Schools, Green- 

 wich, by the Rev. George Fisher. The stone pedestal, on which this 

 instrument was placed, is, by actual measurement, 560 feet, or 0^*6 west 

 of the transit-instrument at the Royal Observatory, which quantity is, 

 of course, applied to determine the Greenwich error. In determining 

 the difference of longitude in the present case, I use the methods which 

 I employed, first, in my journey for the same object between Green- 

 wich and Paris, and subsequently, in the other experiments which I 

 have made to determine the difference of longitude between Greenwich 

 and Oxford, Dublin, Armagh, Edinburgh, Cambridge, &c. The first 

 method is by means of the travelling rate, the second is by the station- 

 ary rate^. The "travelling rate" is the mean rate during the voyage, 

 obtained by dividing the difference between the previous and subse- 

 quent errors at Greenwich, by the number of days absent. The " sta- 

 tionary rate" is a mean of the rates determined, 1st, at Greenwich, 

 before the chronometers were embarked ; 2nd, at Brooklyn, after their 

 disembarkation there ; and 3rd, at Greenwich, on their return, after 

 their landing. The first method is, no doubt, the more unexceptionable 

 of the two ; it involves, indeed, the supposition of the outward-bound 

 rates being the same as the homeward-bound ones ; yet as errors, arising 

 from the magnetic action of the iron in the vessel upon the chrono- 

 meters, or other causes, would, in all probability, be in excess and 

 defect to the same amount, we might therefore reasonably expect a 

 compensation of errors to occur, or nearly so. It is very remarkable, 

 that on board the steam-vessel in all the chronometers, the mean " tra- 



* These have been sometimes called the "shore rates" and the " ship rates." 



