fcT 



S U' N 



And hence arifcs what is frequently obfcrved by fai- 

 lors, viz. That when the Sun radiates obliquely upon 

 the fea, as in the evening, there is no enduring his 

 rays, by reafon they are all reflefted from the water, 

 and fcarce any loft therein; fo that the reftitude or 



obliquity of the rays contributes very confiderably to 

 thecolleftingoffir^. ^ ^y;- I ""- - ' 



And this obliquity, &c. is to be confidered in a two- 

 ' fold refpeft, both with refped: to the matter in the at- 

 mofphere, and to the furface of the eartli'. .* *, 

 Now heat may be varied tv;o ways ; ■ ' *■ ■ - ■ 

 I. By means of the atmofphere, for this does not 

 always remain the fame. '" Thus, e. g. Water is natu- 



■ rally tranfparent, and if you warm it, it ftill retains 



• its tranfparency ; but if you make it boil,' the viapbur 

 "- iflTuing from it, though perhaps a million of times 

 " rarer than the primitive water, will not be tranfparent, 

 '- but opaque, by reafon its parts fiow are under a dif- 

 -ftrent arrangement. -^■- ''^ V' -^ ' •^:'' '^' -' 



' And hence thofe. legions^ of ^corpufcies every where 

 \ floating in the vaft recepucle of the acmofphere, 



■ whenever they acquire 'a different' difpofitidn^ which 



• they frequently do, alter the collection of the rays on 

 the earth.;* Add, that thofe white clouds," which'ap- 

 pear in fumnier time, are as 'it were fo many mirrors, 



'■ and occafion excefTive heat. * . - ;■ .■ ■;» v i'^ 



* ^ t B ' . *- ^ f j^ rf ^p 



' Thefe cloudy mirrors are fometimes round, fjme- 

 times concave, polygonous," &'c. Whefi tM face* of 

 the heaven is covered wit;h fuch white clouds^ the Sun 

 ihinins; amonc^ them' muft oTrieceflity 'create a" great 



■ heat, fince many of his rays, which would otherwile 



■ perhaps never touch- our earth, ^re hereby reflefted 

 to us. Thus, if the Sun be on pne fide, and the 

 clouds on the oppoiite one, tney will be perfect burn- 

 ins-slaire§i^^''And hencelhet)h^nomena of thunder, 



puurs aiiu cxnaiacions, emitted tncrerrom, nev 



by the Sun's affion above a mile high.' But th( 



-mountains a mile and a half high ; to the tops o 



r 

 ^^i.'"- 



^ _ V- 



I have,'?afsi5r/Boerhaave,'obferved,' a kind of hol- 

 ■ low clouds full of hail and fnow, during the continu- 

 ance of which the heat was extreme, fince, by fuch 

 condenfation, they were enabled'to refled: much mor^ 

 ftrongly ; after this came a fharp cold, and then the 

 clouds difcharged their hail in great quantity, to 

 ■which fucceeded a moderate warmth. Frozen, con- 

 - cave clouds therefore, by their great reflexions, pro- 

 duce a vigorous heat, and the fame, when refolved, 



exceffive cold. ^ „ ^r * ^*# ^■;^-^.^';----is.::-r '- 

 Hence it Is probable, thatth^der is only produced 



when fuch concave clouds, before convolv^ed into 

 fpherical figures, are driven wFth bppofite^imotiohs 

 againft each ether, and the rays tranfmitted through 

 thofe fphercs from burning foci. 



* — 



All clouds, it is probable, contain fnow andice, but 

 thefe in their fall through the warmer regions of the 

 atmofphere near the earth, liquefy and diftil in drops. 

 The meteors in the atmofphere have likewife their 

 fliare in reflefting of fire.^ Thefe, in effeft, are a 

 fort of wandering fire vifible by night, and which de- 

 termine the fire over and upon the earth. \ * '"■ ' 

 2. It is varied by means of the earth j for, as the fur- 

 face of the earth varies, fo muft the heat. Thus 

 fandy places, rcflefting more rays than others, muft 



rcater degree of heat. ■ " ' '' ^ " 



excite a g 



On the hicrhcft mountains we. always find the moft 

 cold, fnow,, and hail. '*-V- -. <. i ■•'-"' ' ^;/; ■■ ; 

 In the fultry regions of Peru the mountains are all 

 fummer long covered with fnow, by reafon they only 

 receive diixft, and but little refraded fire ;' and the 

 effeft of fire, arifing merely from being determined 

 by the Sun into a parallelifm, is found by computation 

 to be very inconfiderable. For this effefti, as already 

 cbferved, is greater in winter than in fummer. 

 Though the Sun be in his apogee in the fummer, 

 and in his perigee in winter, yet will a night's ice 

 bear it fliining upon it five or fix hours ere it be 

 thawed. • _ , 



And if, as the Sun rifes nearer tov/ard the zenith, the 

 ice and inowat length begin to run, this is not owing 

 to tlie greater force of the Sun, but to the greater re- 

 flexion and collection of his rays from the,circum- 

 fl:ancc3 and pofition of the atmofphere and earth. 



But the highefi: tops of hills are always free fronl 

 fnow; the reafon whereof is, that water, i. e. tlic va- 

 pours and exhalations, emitted therefrom, never rife 



there are 

 f thefe 

 therefore, vapours, and "confcqucndy clouds^ can nc- 

 " ver'mouht.^ -■ " ' ■' -. ' '' ■ ■ 



"''And hence it is, that in very high mountains, as tlie 



;^Pico de Theide in Bohemia, though the middle pare 



'• 'be eternally in'vefted with ice and fnow, and the bot- 



^^ tom'fcorched with intolerable heat, yet on the top 



• you find yourfelf in a pure, thin, ferene air, and view 



^ the cloifds hovering at a confidefable diftance below 



Hence alfo it is, that all thunder is confined 



■1 r> 



you. 



within lefs than a mile's heights 

 A'dd, that 



;!• 



t> 





J- 



ill ca"vcrns", arid "the hollow parts under 

 ground, the heat is found very great, fo that the air 

 is coldeft in thehigheft places, and hotteft in the low- 

 eft, but in the intermediate atmofphere very unequal. 

 '-Heat therefore depends on clouds, mountains, &c. 

 ^ "which reflect the light varioudy, and on the dircftion 

 '^''oT'the Sun'sVays, or the pofition of his body v/ith 

 '^^refped: to us^'^^^ j^^'- : - - ■ ■ >. r ' ■ . ;^ 



^^^ Hence agam we' gather that fire is the univerfal 

 '■'-■(J^ufe of all th^'motions about our earth, for all fiui- 

 - dity depends on fire, and accordingly, in the large 

 -*■ burning- glafl^es, the firmeft bodies become flu'd,'and 

 *^5^ evaporate in furrie ; and the niore fluid any body is, 

 '-'•"'the more it contains, whence it is, that water, dc- 

 -' prived of all its fire, fixes into ice, and when ex-- 

 --pofed afrefh to the fire rcfolves into water ; and all 

 ■■''fiuids whatever, if deftitute of fire, would do the 

 lame. - ^ ■."_ . i .■.,_.. .- :'.'■- 



■The'Si3n'mify''be'^accounTed the parens natura:?, or 

 " "the primum mobile of all vegetative motion. ' . ^'- 

 ' "^The Sun's attraftive virtue is very confpicuous in' 

 the' exhalatibn of thofe' chide and unwholeforrte va- 

 ^pours, with which the earth is often infefted, which, 

 if they were fuffered to continue long upon the face 

 ' of the earth, v/ould render it a miferable defart. 

 ^The Sun, by fublimating thofe crude and hurtful va- 

 -- pours'," 'and their being rarefied before their defcenfion 

 and diftributiori, forms them into rain, which is of 

 great confequence in vegetation. 

 To this may be added the attraftion of plants them- 

 felves, which creates a kind of emulation in tliem, 

 =^'which fliall grow the talleftr r^^^w ,"^r^ '^^. uu^x^J^ 

 ' But that which the ancients'^iifed to attribute to at- 

 ' trj6i:iol^"'1?ray rio'w be very well folved by piilfion. 

 To apply which to the maTter in hand: when the 

 furface of the fea, &c. is divided by the heat of the 

 ' -Sun^ 'and thf power of the air, their afcenfion thro* 

 ^ the atmofphere, either by the rarefadlion of the air 

 'by the Sun, or otherwife by the refpiration of the ter- 

 "raqueous globe, which in this cafe may be fuppofed 

 ^to aft like the body natural'-, or elfe, that the air, 

 being rarefied by the Sun beams, does, by the gra- 

 vitation' of his' own body in general, force thofe hu- 

 mid vapours by pulfion upward, through thofe beams 

 y or rays of light, which are, as it were, fo many pipes 

 ' of tubes for their ready paflage, afcenfion, and con- 

 veyance. ,- . ■ ' 



■ Or if thofe vapours are conveyed by the undulation of 

 .' the air in a perpendicular manner, rather than a. ra- 

 diant one, through the rays and beams of light, 

 which foever of thefe ways it is, the Sun is the princi- 

 pal agent in, this bufinefs,* and the whole procefs is ci- 

 ther attradion, pulfion, or refpiration, forwarded by 



■ the virtual power of it. - 

 That the rarcfaftion of the air by heat is a great help 

 to attraftion orpulfion may be difcovered by the fire 

 engine made by Mr. Savary. ■ We cannot fay that the 

 water is either forced or attracted by the heat, but 

 that the air that is in the pipe is lengthened by its rare- 

 fying quality to fuch a degree, that the equihbriuni 

 is loft, and the impulfe and prefllire of the air which 



•is without, forces the water to that great height that 





is feen in the operation. 



And fo, if a little fcrip of paper burning and fuming 

 be put into a common drinking glafs, and it be turn- 

 ed 



