576 
Mr. Airy on the 
would produce exactly the same effect by disturbing the 
levels of the transit or other instruments used to obtain the 
time. The immediate effect of such observations then, would 
be merely to confirm or to refute the conclusions deduced 
from the observations of azimuth : if the observations of 
Dr. Tiarks should be considered free from objection, they 
would serve to establish, or to destroy the belief, that local 
attraction may produce sensible disturbances in longitude. 
G. B. AIRY. 
Since the above was written, I have been favoured by 
Captain Sabine with a more detailed statement than I had 
before seen of the extent and probable circumstances of an 
arc in Spitzbergen. It appears that an arc might be mea- 
sured extending nearly from latitude 7 6° 25' to 8o° 35 the 
extremities of which w'ould be on islands at a small distance 
from the main land of Spitzbergen. With the same formula 
as before, the error to be used in the method of least squares 
would be 
— measured length -j-Mx 15000 — N x ,1338 + P x ,201. 
Upon comparing this expression with those given before, it 
will be observed, that this is the only error in which the 
coefficient of N has a large negative value ; and that from 
the preponderance at present of negative signs in the coeffi- 
cients of P, an error with a positive coefficient of P would be 
very desirable. On these accounts then, an arc of that extent 
in that latitude would contribute much to our knowledge of 
the figure of the earth. But it is very likely that there would 
be sensible disturbances in the latitudes of the extreme 
