(252.) 
Russian are operation very lately executed in Russia and other 
by M. 
Struve. 
(253.) 
Its extent. 
(254.) 
(255.) 
Details of 
the Russo- 
Scandina- 
vian Are. 
854 
count of it, published at the East India Company’s 
expense in 1847. The heats and the rains, the 
dull opake atmosphere of the Doab, with its bound- 
less and densely-wooded flats, the jungle fever and 
the wild animals, were natural impediments enough. 
But Colonel Everest, whose conscientious anxiety 
reached almost a nervous pitch, seems not to have 
been satisfied with any one instrument which the 
mechanicians of London could produce ; but to 
have metamorphosed most of them, partly with his 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. VI. 
tending over dead flats have, in the southern part of 
the are (as in India), occasioned great difficulties, and 
compelled the erection of numerous temporary struc- 
tures to overlook the country. In the north the 
extraordinary refractions have, as usual, created some 
difficulties. Ten different base lines, all at a small 
height above the sea, form part of the operations. 
It is a very satisfactory cireumstance, that by the 
care of M. Struve and Mr Airy, the standards of 
length used in the Indian and Russian ares have 
been directly compared. ‘ 
The calculation of the figure of the earth from the 256.) 
completed Russian are, in combination with others, General re- 
has not yet been made, but it is believed that it phayead 
will indicate an ellipticity somewhat greater than ellipticity 
that generally received. The results obtained by Co- from geo- 
lonel Everest, on the other hand, by comparing his 25 
are with those of Europe, give generally small ellip- 
ticities, that is under ,3,. The French and Indian 
arcs, for instance, give 344. Now Mr Airy had de- 
duced 20 years ago from the best existing observa- 
tions y},; Bessel, a few years later, obtained the al- 
most identical result of -}5; and Schmidt of 53 ,. 
The determinations by means of the pendulum are and from 
somewhat larger. The extensive observations of Co- pendulum 
lonel Sabine and Captain Foster concur in giving eee 
an ellipticity of 54; but the French experiments by oz 
own hands, partly by native aid. It says much for 
his ability in this respect, that the results appear 
entitled to compete with all the most exquisite of the 
kind in Europe. His bases, for instance, about 74 
miles in length, when checked by intermediate trian- 
gulation above 400 miles in extent, differed in one 
instance by 4, in another by 7 inches from the pri- 
mary measurement. The whole extent of Lambton’s 
and Colonel Everest’s operations includes a continu- 
ous arc of 21° 21’ (1477 miles), by far the greatest 
at that time executed. 
It is indeed only rivalled in this respect by a vast 
northern countries of Europe, by which an arc of 25° 
20’, extending from the banks of the Danube to the 
shores of the Arctic Sea, near the North Cape, has 
been measured under the general superintendence 
and direction of that able astronomer M. Struve, 
whose meritorious labours in other departments of 
astronomy will be specified in’ a succeeding section. 
The results are still incomplete, though the opera- 
tions in the field were happily concluded just in time 
to prevent their total frustration by the unhappy war 
in which Russia has since engaged. 
The arcs of India and of Russia include a space 
from Lat. 8° to Lat. 71°, with the exception of only 
about sixteen degrees, and are unquestionably the 
most important which exist for the determination of 
the earth's figure. When to them we add the French 
arc of 12° 22’ in a medium latitude, it will scarcely 
be necessary to take into account any other, at least 
for the Northern Hemisphere. 
The following brief details of the Russian are are 
taken from the provisional report of M. Struve (1852). 
The southern extremity of the Russo-Scandinavian 
arc is Ismail on the Danube (Lat. 45° 20’), the north- 
ern extremity is Fuglenaes on the island of Qualoe 
in Finnmarken (Lat. 70° 40’). The interval from 
Tornea to Fuglenaes (4° 49’) was measured bySwedish 
and Norwegian engineers; all the remainder by those 
of Russia, and, in particular, by M. Von Tenner, who, 
with M. Struve, has since 1816 directed the whole 
operation. The whole line is remarkably freefromcon- 
siderable inequalities of ground, and from mountain 
ranges, so that local attractions are probably incon- 
siderable.! On the other hand, extensive forests ex- 
Duperrey and Freycinet lead to a result considerably 
greater. The discrepancy between the geodetical and 
pendulum results may of course be a real one de- 
pending on local variations of density. The astro- 
nomical determination from the lunar inequalities, 
which might be expected to concur with the results 
of the pendulum, gives (as we have seen in the chap- 
ter on Physical Astronomy, Art. 63) 335 at a mean. 
J regret that my limits do not permit me to speak  (257.) 
of the measure of degrees of longitude or ares of pa- 4 itieh a 
rallel, as another test of the earth’s figure. The re- ? 
sults, however, cannot compete in point of certainty 
with those from ares of the meridian, It may be sa- 
tisfactory to add, that the British are of parallel from 
Greenwich to Valentia (west coast of Ireland) sen- 
sibly accords with the earth’s figure obtained inde- 
pendently. 
In connection with the subject of the pendulum 258.) 
treated in the earlier part of this section, I shall here M- Fou- 
mention a very remarkable experimental observation 
the 3d February 1851, by M. Léon Foucault, to 
whom we also owe some ingenious experiments on 
the velocity of light. It is not indeed connected with 
the determination of the earth’s figure, but it has a 
connection with astronomy, inasmuch as it affords the 
most remarkable and direct proof of the earth’s rota- 
tion round its axis. 
1 In India, on the contrary, the local attractions of the Himalaya must be very sensible ; indeed Mr Pratt has calculated them 
to be so considerable, as to have given rise to a curious speculation by Mr Airy as to the circumstances which may tend to 
diminish the attraction of mountain rang es.— (Phil. Trans. 1855.) 
cault’s pen- 
3 2 : dulum ex- 
communicated to the Paris Academy of Sciences, on periment, 
