THEORT of RAIN. 57 



2. Of the Regularities of Rain. 



THE variable rains and falls of fnow, which happen irregularly 

 in moft places, having been explained from the natural conftitu- 

 tion of this globe, from the proper difpofition of its folid and its 

 fluid parts, and from the periodical influence of heat and cold, 

 occafioned by the motion and poiition of this globe, in relation 

 to the fun, we mall find it eafy to underftand the more regular 

 periodical appearances, with regard to rain, which happen in a 

 few places of the earth. 



IN looking for a regular periodical caufe for the mixture of 

 portions of die atmofphere, in different degrees of heat, and fuf- 

 ficiently faturated with humidity, nothing appears fo promifing 

 as the trade-winds in the Indian fea, blowing one half of the 

 year in one direction, and, during the other half, in a contra- 

 ry direction ; for, as thefe ftr earns of atmofphere are limited, 

 they muft ibmewhere produce a mixture of different portions 

 of that fluid mafs j and, in finding rain to be the confequence 

 of thefe regulated events, or as correfponding to thefe probable 

 caufes, we mall have reafon to conclude, that thofe mixed por- 

 tions of the atmofphere have been fumciently faturated with hu- 

 midity, and in different temperatures, in relation to heat. But 

 this is actually the cafe ; we find, in this place, regular appear- 

 ances, with regard to rain, which correfpond to the regular 

 caufes now afligned, for the commixtion of the atmofphere. 

 This correfpondency, therefore, while it explains thofe natural 

 appearances, confirms the theory. 



THE iflands which are placed under the line, in the middle 

 of the Indian ocean, feem to form for themfelves conditions of 

 periodical condenfation, that correfpond to the diurnal influence 

 of the fun, and to the noclurnal motions in the atmofphere. 

 It is not here pretended to explain, a priori, how, in fuch places, 

 either always, or at certain feafons, there fhould be daily periods 

 of rain. It is enough to find that fuch is the fai, and that 



H it 



