BOUGUER^S VOYAGEi TO PERU. 293 



m proportion as it removes from the equator, it will touch the earth beyond the two 

 polar circles, though our calculations have regard only to the fummer. 



This \me may be called that of the Conftant Lower Boundary of the Snow, for 

 there mud neceflarily be another, i. e. the Upper Boundary ; but this, to all appear- 

 ances, the highefl mountain of the world does not reach. If there were mountains 

 high enough to lift their fummits above all the clouds, the more elevated parts of thefe 

 high fummits would be free of fnow, and we fhould there enjoy, could we attain the 

 ftation, a perfect and perpetual ferenity, as is improperly conceived of Olympus, Mount 

 Ararat, and of Theyde, or the Peak of Teneriff, although the latter does not completely 

 reach to the lower boundary of congelation. To limit myfelf firaply to declare here, 

 what I myfelf proved, fome of the mountains which have ferved as ftations for our 

 triangles, Cotopaxi for inftance, have a portion covered at from fix to feven hun- 

 dred toifes of perpendicular height. It will be unneceflary to mention others along our 

 meridian, as well as on both fides the river Magdalene, approaching the fea from the 

 north, to Saint Martha. Chimborazo, which is the highefl of all I have noticed, or 

 even feen, is three thoufand two hundred and feventeen toifes above the fea, and the 

 part of it on which the fnow lies more than eight hundred. But if the clouds fome- 

 times pafs lower, which opens the fummit to our view, they alfo pafs fometimes con- 

 fiderably above the fummit, even to three or four hundred toifes, which has enabled 

 me at a diftance to judge of them, comparing their height with the dimenfions of the- 

 mountains I had already meafured. In a word, the fpace, in the perpendicular or ver- 

 tical fenfe, between the two boundaries, the upper and lower of the fnow, is at leaft, 

 in the torrid zone, eleven or twelve hundred toifes ; we mufi: even confiderably add to 

 this height, if it is permitted us to confound the clouds formed by the fmoke of the 

 volcanoes with others, for I have obferved it afcend feven or eight hundred toifes ftill 

 higher. Thus, if we fhould flop at this lafl boundary, and there had been mountains 

 high enough, a girdle or zone of ice might have been noticed, the beginning of which 

 would have been at two thoufand four hundred and forty toifes above the level of the 

 fea, and ending at nearly four thoufand three hundred or four thoufand four hundred 

 toifes ; not that we are to conclude from hence the ceflation of the cold at this point, 

 fmce it is certain, on the contrary, the farther we are removed from the earth, the 

 greater will be the degree of cold, but by reafon that the clouds or vapours cannot 

 afcend higher. 



It is not difficult, by a little attention, to be convinced, that the col^ mufl na- 

 turally increafe in the proportion we are lifted into the atmofphere. It is not only the 

 firfl obflacle to our afcending, but alfo to our breathing, in a very great elevation, had 

 we the power to reach it ; a circumflance which has not enough impreffed the minds- 

 of thofe, whofe ideas have led them to conceive and talk of an agreeable refidence above 

 the region of the clouds. It had been reafonable, in order to defcribe the cold felt: 

 upon the fummit of mountains, to infifl upon the fhort duradon of the power or aftion 

 of the fun, which falls but for a few hours upon each of their fides, and frequently not 

 at all. An horizontal plain, when the fky is clear, is fubjeft, in the middle of the day, 

 to the perpendicular aftion of his rays, the force of which nothing can diminifh : whereas 

 an inclined furface, the fides of an high point of rocks, almoft perpendicular, can only, 

 be played upon by them. But let us confider for a moment an infulated point, in the. 

 midfl of an elevated atmofphere, and draw an abflraftion from all mountains, and even 

 clouds which float in the air. 



The more diaphanous the centre may be, the lefs of. heat it will imbibe froni the im* 

 mediate adion of the fun. The facility with which a very tranfparent body gives paf- 



fage 



