the cavern at Praya Formosa, close to the sea, about three miles
west of Funchal, and upwards of thirty feet deep, I found a
difference of only 3° F. and in that of St. Roque, about 1000 feet
above the sea, north of Funchal, and nearly sixty feet deep, a
difference of only 4° F.
There is an extraordinary difference, however, between the temperature
of the wells and that of the air of Funchal; the former
(Mr. Lundie’s, Mr. Young’s, and Mr. Serle’s, all upwards of
twenty feet deep and in the open air) being 58° when the latter
was 69°—but this is explained by recollecting, that these wells are
supplied by streams which descend from heights of 3800 feet
behind the town, where there would be a corresponding difference
in the mean temperature; for that of the spring near the Mount
Church, (enclosed at the expense of Consul Murray) and about
1900 feet above the wells in question, was 58°, the air within
being 62°, by an observation which I made in 'October. The
observations on the Peak of Ruivo gave eighty-nine toizes to a
centigrade degree, for the decrease of temperature ; those on the
brink of the Coural, at the point of view from which the drawing
was made, ninety-five toises; those at the Mount Church, ninety-
eight toises; the two latter results are probably in excess, from
the elevations being backed by greater height, and not at all
insulated. I have calculated in toises, merely because the results
of De Humboldt’s and De Saussure’s' observations are given in this
measure. When at Arieiro, a cold north wind came on to blow
suddenly, and lowered the thermometer so considerably for the
time, that I could make no conclusions; and the locality of
Mr. Veitch’s quinta is such, from the torrents adjoining it on. each
side, that it is much colder, as a particular spot, than the country
about it, and at the same height above the sea. November seems
to be the month whose mean temperature is the closest approximation
to that of the year in these regions.
The mean of thirty-eight observations in the month of November
in Funchal, 154 feet above the sea, at 8J a.m. 2 p.m. and sunset,
by Leslie’s hygrometer was 3.2 ; of 41 by de Saussure’s, 65.1 ;
of 24 observations in December, by Leslie, 3,1 ; of 37 by De Saussure,
75.3 ; of 31 by De Saussure in January, 83.3. During a very
strong wind in the month of November De Saussure’s fell from
71 to 50 within five hours : its maximum of dryness during my
observations was 41° (in the morning of the 22d pf November)
the thermometer being at 19 C. or 66,2 F., and a correspondent
observation with Leslie’s hygrometer giving 5.3f. De Saussure’s
stood at 57° on the Peak of Ruivo, before the clouds had ascended,
the thermometer being at 49 F., at which time (10. a,ça,) Leslie’s
descended to 2.4 at Funchal, (equal to 85° of De Saussure’s, from
a comparison of numerous, coincident observations,) the thermometer
being at 68J° : now if we reduce the former observation
to the same temperature as the latter, taking the results of the
experiments of De Saussure for ascertaining the weight of moisture
contained in the air at different degrees of the thermometer and
hygrometer, for the data of our calculation8, the 57° of Ruivo
becomes 46f° which gives but 162 feet to each degree for the
decrease of humidity in this region \ Snow descends in Madeira
'Lieutenant Colonel Franzini informed me, that no hygrometncal observations had
been made in Lisbon. I made the following, during my stay there in September :
8. a.m. mean of 21, Saussure, 71.3 ; of 19, Leslie, 3.7 ; of 19, Thermometer 71. F. ;
2. p.m. mean of 19, S, 61 ; of20, L. 6 ; of 18, Thermometer 75.6: 9. p.m. mean of
17, S. 67 : pf 16, L. 5.6 ; of 16 Thermometer 71.8. The minimum of my observations
was 23.5 S. a porresponding observation of Leslie giving 11J ; Temperature
801, September 4th, at 2, p.m.
s Essais sur VHygrométrie, Neuchatel, 1783. p. 181.
h I endeavoured to procure De Saussure’s cyanometer through professor Pictet, but
unsuccessfully, the inventor’s standard being lost ; the accurate degradation of blue
oyer the whole circumference of the apparatus, and the absolute similarity of the tint
or shade of a given division of the copy with that of the same number in the original,
S