REPORT ON ASTRONOMY. 
167 
measure was erroneous : but tlie result of MM. Plana and 
Carlini’s measure is still anomalous; perhaps not more so than 
the form of the country would lead us to expect. I may men¬ 
tion here that Zach, in the Monatliche Correspondents and in 
the Correspondance Astronomique , has shown clearly that Lies- 
ganig’s measure is worth nothing. An arc has been measured 
by Gauss from Gottingen to Altona, of 2 degrees; the as¬ 
tronomical observations being made with Ramsden’s zenith- 
sector ; some accounts of it will be found in the Ast. Nadir., 
and in a small work entitled Bestimmung des Breitenunter- 
sdieides , 8$c. An arc of o-J- degrees has been measured by 
Struve, the northern extremity being on an island in the Gulf 
of Finland. In many parts of this operation, new instruments 
and new methods have been used: in particular, for the deter¬ 
mination of the latitudes, great reliance was placed on the 
method of observing stars with a transit instrument whose 
motion is confined to the prime vertical: accounts of this 
measure are in the Astronomisdie Nackriditen . The distance 
on the arc of parallel between Dover and Falmouth having 
been ascertained in the course of the English survey, and 
the difference of longitude between them being determined, 
by Dr. Tiarks, by the transportation of chronometers, the 
length of an arc of parallel for one degree in a definite latitude 
is found, and this determination assists much in determining 
the earth’s figure. But a far longer arc of parallel has been 
measured, on the Continent, from Marennes (near Bordeaux) 
to Padua. The geodesic part of this measure had been nearly 
completed by the French Government, while the country was 
in their possession ; all that was wanting was to connect the 
surveys on opposite sides of the Alps. This was effected 
(though not without difficulty,) by Austrian and Sardinian 
officers. It was then necessary to determine the difference 
of longitude of the extremities. This was done by dividing 
the arc into six portions, in each of wdiicli a point could be 
found visible at both its extremities, and observing at each 
extremity the absolute time at which small quantities of gun¬ 
powder were fired at the middle point. The French part was 
undertaken by MM. Nicollet and Brousseau: the rest by 
MM. Plana and Carlini. The result thus obtained is perhaps 
liable to considerable doubt, as the errors of all the different 
observations are accumulated. It is unfortunate that the dif¬ 
ference of longitude of the extremities has not been determined 
without any intermediate determination. 
The above, as far as I am aw r are, are all the measures that 
have actually been made within the present century. But there 
