198 
‘supposes such incessant self-denial, is 
fit only for Utopia. I am quite sure 
those who usually put this question 
would never think of acting on it them- 
selves. B. 
———— 
To the Editor of the Monthly Magazine. 
SIR, 
A he the 5th of an interesting series of 
“ Letters from the South of Italy, 
by a recent traveller,”’ (p. 506 of your 
last vol.) a very circumstantial account 
is given of that “ wonder of nature,” 
Mount Etna. In that letter the tra- 
veller censures the method of measur- 
ing the heights of mountains by the ba- 
rometer; and (p. 508, note,) gives an 
observation, aud a trigonometrical cal- 
culation founded thereon, from which 
results “ for the axis side of Etna four 
miles and twenty-four eighty-fourths, 
above four miles and a quarter, or 
about twenty thousand four hundred 
(22628) feet for the total height. This 
measure,”’ says the traveller, “is not 
perhaps perfectly correct, but, at least, 
it approximates very near to it (cor- 
rectness.) If this height appears sur- 
prising,”’ he continues, “ we ought to 
consider that other great mountains 
have never been measured but with the 
barometer, and that Mr. Brydone was 
surprised to see the mercury here de- 
scending nearly two inches lower than 
on the summit of the Alps.” 
The height thus determined does cer- 
tainly appear surprising; it so much ex- 
ceeds the heightassigned toEtna byevery 
other observer (with the exception per- 
haps of that visionary, Kircher, only,) 
that an enquirer, without questioning 
the greater correctness of the trigonome- 
trical, when compared with the baro- 
metrical method of measuring altitudes, 
would be inclined to suspect some in- 
accuracy in the observation, or error in 
the calculation made by the traveller. 
With respect to the former, it does not 
appear very probable that an observa- 
tion made at the distance of sixty miles, 
and that distance perhaps not ac- 
curately ascertained, can furnish data 
sufficiently correct for a near approxi- 
mation to the true altitude of Etna; 
and with respect to the latter, it will 
be found that the caleulator has erred 
by employing in his calculation the 
arcs or measures of the angles of his 
triangle, instead of their sixes ; which, 
except in very small arcs, differ con- 
siderably ; and when the two angles 
are very unequal, as in the ease under 
consideration, are far from being pro- 
Comparative Heights of Mouniains. 
[April 1, 
portional. Correcting a slight typogra- 
phical error (66 being printed for 60) 
and employing the sines of the angles 
instead of the angles themselves, the 
proportion given by the traveller will 
stand thus: 
Sin. 84° Sin. 6° 
9915219 *99™? I. 1045245 
Bat the calculation may be facilitated 
by substituting the following propor- 
tion for that of the traveller : 
S ¢ 0 
Ralls.) 60. m.:: {Yostosat : 630625 m.* 
Hence it appears that the result, 
when correctly deduced from the data, 
(iustead of being 424, that is 4? miles, 
or 22628 feet, as determined by the 
traveller,) amounts to the still more 
astonishing- height of 6°30625 miles, or 
33297 feet. This result is more than 
three times the height assigned to Etna 
by Sir George Shuckburgh or Saussure, 
whose respective measures are 10954 
and 10965 feet, and are probably the 
most correct of any yet given. It is, 
therefore, very evident that the tra- 
veller, however accurate and luminous 
his descriptions in general may be, (and 
the present writer readily acknowledges 
his admiration of them,) has erred in 
one or both of the dataft on which his 
calculation is founded. 
Respecting the barometrical method 
of measuring altitudes, the writer of 
thearticle Barometer in the Edinburgh 
Encyclopedia, says ‘* The results ob- 
tained by means of this instrument ap- 
proach so near to perfect accuracy, 
when all circumstances are properly = 
estimated, that this method of deter- 
mining the heights of mountains is, in 
many cases, even preferable to the geo- 
metrical methods.’? Though some 
persons may not be disposed to agree 
with the encyclopzdist, yet it must be 
acknowledged that ** the custom of 
calculating the elevation” of mountains 
“ with this instrument,’ when applied 
conjunctively with the thermometer, 
according to the precepts laid down by 
i :6°30625 m. 
* In the former of these proportions the 
result, as is well known, is more expedi- 
tiously known by logarithms. In the lat- 
ter the logarithmic process offers no ad- 
vantage, as it requires three inspections of 
the tables ; whereas only one inspection is 
required when logarithms are not employ- 
ed;—that for the purpose of taking out 
the natural tangent of 6°. 
+ No allowance appears to have beea 
made for refraction, though its effect in 
elevating very distant terrestrial objects is 
by no means inconsiderable. 
De 
