New Method of determining the Longitude. 109 
adopted, at one and the same time, by persons in every 
habitable part of the globe ; forit is applicable to situa- 
tions distant 180° in longitude from each other, and even 
beyond that distance, as I shall show by one of the subse- 
quent examples. 5. 
The longitude of a place may be deduced from obser- 
vations made on the culmination of the moon and stars by’ 
calculations depending on the tables of the moon and stars ; 
in which case, the correct time must me erred and the 
errors of the tables are involved. r. Baily, in this 
paper, speaks only of corresponding peeve, ; that is, 
observations of the same bodies made at different obser- 
vatories. In this case “‘ it will not be of any consequence 
if the clock should not ezactly show the correct time; as 
it isthe difference only, between two given moments, that is 
required. All thatis necessary therefore is, that the clock 
should go correctly during the short interval of the tran- 
sits. In fact, the whole method is a method of diffe 
only; and itis to these ea ei: that the principal at- 
tention must be paid.’ 
ethod of obtaining the longitude was first success- 
fully, sd not till recently, practised, by M. Nicolai, a 
distinguished astronomer at Manheim. He s subsequently 
ublished a list of stars that can be favourably situated 
or corresponding observations of this kind, and invited the 
co-operation of other observers. These stars he calls 
moon-culminating = sles wish he had chosen a better 
term. The result of this proposal was, that successive 
lists of such stars were published, “ and already, at several 
observatories, the observers have been to deter- 
mine their difference of meridian, ina few months, with as 
much accuracy as they formerly could in as many years. 
It might, indeed, at first sight, appear that the same re- 
sults would be obtained, if we merely observed the correct 
time of the moon’s transit, without any reference to the 
contiguous stars: but a moment’s re ion will convince 
us that, by referring the moon’s border to the adjacent 
stars, we Obviate all errors net only of the clock, but also 
in the position of the transit instrument.” —p 
The last circumstance mentioned above, relating to the 
position of the transit instrument, will be regarded as a 
important advantage possessed by Tap taethod ; especially 
