In the month of May the rains commence, not with the fury of a deluge, as in the months of August and September, but heavier than any rain experienced in Europe.  Peals of thunder reverberating through the mountains give a warning of their approach, and the sun breaking through the clouds promotes the prolific vegetation of the fields with its vivifying heat.  The heat at this season is equal to the summer of Europe, and the nights are cool and pleasant; but the dews are heavy and pernicious to health.  The following meteorological observations, carefully made by Don Jose Ma.  Vertez, a Captain of the Spanish navy, will exhibit the average range of temperature: 

Ds of heat observed in the capital of Porto Rico, taking a medium of five years.

Degrees of Heat Observed in the Capital of Porto Rico, Taking a Medium of Five Years.

Hours of the Day.     Jan.  Feb.    Mar.  Apr.  May.  June.  July.  Aug.  Sept.    Oct.   Nov.  Dec. 
Seven in the morning  72  72 1/2 74   78   78    82    85   86    80 1/2  77    75   75
Noon                  82  81     82   83   85    86    90   92    88      85    84   80
Five in the evening   78  74     78   80   81    84    87   90    83      82    80   79

The weather, after a fifteen or twenty days’ rain, clears up and the sun, whose heat has been hitherto moderated by partial clouds and showers of rain, seems, as it were, set in a cloudless sky.  The cattle in the pastures look for the shade of the trees, and a perfect calm pervades the whole face of nature from sunrise till between 10 and 11 o’clock in the morning, when the sea breeze sets in.  The leaves of the trees seem as if afraid to move, and the sea, without a wave or ruffle on its vast expanse, appears like an immense mirror.  Man partakes in the general languor as well as the vegetable and brute creation.

The nights, although warm, are delightfully clear and serene at this season.  Objects may be clearly distinguished at the distance of several hundred yards, so that one may even shoot by moonlight.  The months of June and July offer very little variation in the weather or temperature.  In August a suffocating heat reigns throughout the day, and at night it is useless to seek for coolness; a faint zephyr is succeeded by a calm of several hours.  The atmosphere is heavy and oppressive, and the body, weakened by perspiration, becomes languid; the appetite fails, and the mosquitos, buzzing about the ears by day and night, perplex and annoy by their stings, while the fevers of the tropics attack Europeans with sudden and irresistible violence.  This is the most sickly season for the European.  The thermometer frequently exceeds 90 deg.  The clouds exhibit a menacing appearance, portending the approach of the heavy autumnal rains, which pour down like a deluge.  About the middle of September it appears as if all the vapors of the ocean had accumulated in one point of the heavens.  The rain comes down like an immense quantity of water poured through a sieve; it excludes from the view every surrounding object, and in half an hour the whole surface of the earth becomes an immense sheet of water.  The rivers are swollen and overflow their banks, the low lands are completely inundated, and the smallest brooks become deep and rapid torrents.