I had taken the angle of elevation of the Peak of Ruivo with a
reflecting circle, from the point generally visited by strangers for
the best view of the Coural, and adjoining the Pico das Bordas,
knowing that I could get its horizontal distance from Ruivo very
accurately from Lieutenant Colonel Paulo Dias d ’Almeida’s survey,
just completed, after six years’ labour, drawn originally on a scale of
twenty-eight inches to a Portuguese league, and containing every
qrnnta on the island. My own attempts to get a sufficient base by
angles from a smaller one, measured with the aid of an artificial
horizon of crystal, and a proof telescope, (lunette d’epreuve,) failed
from unfavourable weather.
6 6 20 Apparent angle of Ruivo.
26 Refraction“.
6 5 54 Which, with 24,805 feet for the horizontal distance, gives 2578
Height of apparent, above true level, for 24,805 feet . . . 15
Height of point of view above the level of the sea . . . ‘3710
Height of Ruivo 6303 being 139 feet more” than that given by the barometer, which was
Fortin’s, and had been compared with that of the observatory for
several weeks. M. Von Ruch, and Professor Smith, found the
Torrinhas (notoriously lower than the Pico Ruivo) 5857 feet
above the sea1. These circumstances considered, I cannot help
* To estimate the terrestrial refraction, (not having Lindenau’s tables of negative
coefficients,) I followed the method recommended, I think by Pictet, at the end of
he first volume of De Saussure’s Travels; calculating (by Dr. Young’s tables) the
astronomical refraction at each station, for the angle of elevation under which Ruivo
is seen from the lower, (knowing the height of the barometer for each,) and taking
the half on the supposition, which may be made without any sensible error, that the
curve between the two stations is circular. This gave me within a fraction of what
Dr. Maskelyne allows, viz., ^ of the intermediate arc: but, if the consideration of
the refraction were neglected altogether, it Would not make a difference of six feet.
’ M. Pictet’s measurement of Mont Blanc, from the glacier of Buet, in a similar
manner, exceeded De Luc’s direct barometrical measurement by 210 feet.
1 Narrative o f an Expedition to explore the River Zaire. Introduction, p. Ixviii.
Ruivo was not accessible at the time of their visit to Madeira.
feeling some confidence in the result of my own observations,
although I observe by Captain Sabine’s recent article in the Journal
of Science, that he'made it only 5438 feet above the level of the
sea. Baron de Humboldt found the decrease of caloric at Tene-
riffe, to be ninety-four toises- for every degree of the centigrade
thermometer; De Saussure, at Etna, ninety-one toises ; my observation
gives eighty-nine toises, or five less than De Humboldt’s ;
but Captain Sabine’s gives only sixty toises for a centigrade degree,
or thirty-four less than De Humboldty: this would seem to be a
further evidence in favour of the greater height of Ruivo.
My next route was northwards to St. Vicente, which is about
twenty-five miles from Funchal, passing first along the brink of
the Coural or ravine, into which I had already descended, and then
on the very margin of a second, scarcely less bold, but less awful,
and much more luxuriant in vegetation. Woods of laurels line
the declivities along which the road is formed, and wooden bridge,
are thrown over the frequent torrents, near one of which the
basalt rock assumes the form and detail of a ruined castle so
happily, that it seems to defy the pencil to draw any thing else.
Beyond this, the distant sheets of broom look like sloping lawns,
occasionally diversified by the mellow brown- of decaying ferns.
Here I first saw the beautiful fern asplenium palrnatum. The
filices form by far the most interesting family in Madeira, verifying
Baron de Humboldt’s remark, that their maximum may be found
in the mountainous parts of small islands; it will be seen that
several are newz, and all were highly luxuriant, yet I was disapy
Temp, at Ruivo, 36° F., at Funchal, eight feet above the sea, 61.5. Journal of
Science, xxix. p. 82.
a For a more particular list of the ferns I must refer my readers to the Appendix,
No. 1. The P. vulgare therein mentioned, I think must be a variety of that species
found at Teneriffe by M. Leschenault. The aspidium palmatum I believe to be rare;