58 WRITINGS OF JOSEPH HENRY. [1855- 



belt of rain, produced by the partial condensation of the 

 vapor which ascends with the air of this region ; and since 

 the sun between the 21st of March and the 21st of June 

 passes from the equator to 23| degrees north, and then 

 makes a similar excursion as far south, the rainy belt follows 

 his course, and hence all countries within the tropics must 

 have a periodical rainy season. 



The air also which flows over to the north, and which, as 

 we have seen, descends to the earth in the westerly belts of 

 wind, carries with it a portion of vapor, and deposits it in 

 the form of rain ; and hence there is a tendency to a rainy 

 and dry season beyond the tropics, which oscillates north 

 and south with the varying motion of the sun. This ten- 

 dency to regularity of rain is in many places masked or 

 neutralized by the configuration of the country. It is how- 

 ever distinctly marked on the western coast of the United 

 States and of Europe, as well as in various other places in 

 the north temperate zone. Oregon and California have 

 their rainy belt, which descends to the south in the winter, 

 and again returns in the spring. In Lisbon, the number of 

 rainy days in December is 15, to 2 in July ; in Palermo, 17 in 

 December, to 2| in July. In Algiers, which is also north of the 

 tropic, but farther south, from the average of ten years, there 

 are 18 rainj'^ days in January, and on the other hand, only 

 a single one in July. Another fact of interest with regard 

 to the extra-tropical belt of rain is that it commences sooner 

 at greater elevations above the surface : for instance, at the 

 peak of Teneriffe, the rainy season commences at the top a 

 fortnight earlier than at the bottom ; so that while rain is fall- 

 ing in abundance on the summit, the country in the vicinity 

 of the mountain, at the level of the sea, is enjoying sunshine 

 and a balmy atmosphere. According to Mr. Espy's views, 

 the latter results from the radiant heat given off by the con- 

 densing vapor above. The sun however descending still 

 farther to the south brings down the rain belt to the level of the 

 earth in this latitude, and the rainy season then commences. 

 Similar phenomena have been observed on the higher parts 

 of the Coast range of mountains of California ; and indications 



