13G EXCURSIONS IN MADEIRA 



to 2500 feet. De Humboldt states 9800 feet, as the least height 

 at which snow falls in the parallel of 20° N. The first snow fell 

 on the 16 th of December. 



The mean of 42 observations at 8.5 a.m. 2 p.m. and sunset, by 

 Fortin's barometer (which had been compared for several weeks, 

 with that in the observatory at Paris) was 767.30. of 43, in 

 December 764.22, of 31, in January 761.60; in a turret 154 

 feet above the level of the sea. As far as I could judge, from 

 a short series of observations during the more settled days of 

 October, the maximum corresponds to 81 a.m., and the minimum 

 to 3, p.m. in Madeira. 



I do not think the mean of the annual quantity of rain which 

 falls at Madeira, can be far short of forty inches. I determined 

 the quantity which fell in January by a series of observations with 

 a roofed pluviometer, so as to prevent any loss by evaporation, 

 and it amounted to 13.2 inches. The heaviest rain was on the 

 24th, 0.96 of an inch in five hours'. According to Dr. Savignon, 

 19.33 inches, fell at Laguna in Teneriffe in 1812, and 25.22 inches 

 in 1813 : if this be correct, the increase from 45° N (where 24i E 

 inches is considered to be the mean annual quantity), to 28° N, 

 would seem to be in a lesser proportion than from 28° N to 19° N, 



were consequently impossible, as well as indispensible conditions. But it was well 

 known, that the class of observations to which the instrument was destined, was not 

 considered by De Saussure as an important and conclusive source of atmospherical 

 results ; the colour and depth of the blue of the heavens being so far influenced by 

 the pressure of the least quantity of vesicular vapour, that nothing certain or absolute 

 could be concluded from its estimate, by a comparison with the slowly degrading 

 shades of the circular divided zone which constituted the instrument, to say nothing 

 of the difficulty of determining by observation, to which of its divisions the blue of 

 the heavens exactly corresponded. 



'31. 5 inches of rain fell in Lisbon in 1816, and 21. 4 in 1817, the palma or 8. P. 

 inches being equal to 8. 9 English; but 1816 was considered an extraordinary year 

 in this respect by the inhabitants. Franzini, b.c. p. 28, 123. 



