41 
Arvr.IV. An Account of some Observations made with Mr. 
Daniell’s Hygrometer, in Brazil, and on the Equator, by 
Alexander Caldcleugh, Esq. 
[Communicated by the Author.] 
On my return from the southward to Rio de Janeiro, the end 
of July, 1821, I was extremely pleased to find one of Mr. 
Daniell’s Hygrometers among some other instruments Mr. New- 
man had sent out; and although from the general dryness of 
that period of the year, experiments on the quantity of humidity 
contained in the air were not likely to prove the most interesting, 
yet I did not consider either this circumstance, or the probable 
shortness of my stay, as affording a sufficient excuse for leaving 
the country without making some observations; and these, im- 
perfect as they are, I have now the honour of laying before the 
readers of this Journal. 
I shall take the liberty, however, of prefacing them with afew 
general remarks on the climate of this part of Brazil. 
The summer begins about the months of October or No- 
vember, and lasts until March or April. This is the wet season, 
but the rains by no means descend from morning till night, as in 
some other tropical countries, but commence, generally, every 
afternoon about four or five o’clock with a thunderstorm. The 
heaviness of the rain can only be conceived by those who have 
been in these latitudes. This fall naturally arrests the sea 
breeze, and the succeeding night is dark and cloudy. Formerly 
these diurnal rains came on with such regularity that it was 
usual, in forming parties of pleasure, to arrange whether they 
should take place before or after the storm. During this period 
of the year there is seldom, if ever, a deposition of dew. 
From April until September very little rain falls: vegetation 
almost stops, and to the eye of every one who has not just ar- 
rived from Europe a wintery appearance is discernible. The 
land and sea breezes do not succeed each other with the same 
regularity, and are besides more frequently disturbed by violent 
gusts from the S. W., imagined to be the tails of those de- 
structive winds the Pamperos of the River Plate. The nights 
are beautifully clear; Venus casts a shadow, and the southern 
constellations are seen in all their beauty. The dews, as might 
be expected, are at this season very copious. The annual mean 
height of the barometer in Rio de Janeiro is about 30,275, and 
of the thermometer a fraction above 73° Fahrenheit. 
