N 



U N 





ed up unmcdiately, and put upon a plate of water, ic i The Sun alio exhales all luperiluous moifturc, and by 



^ * '" ' ■ ■ " 1 r . j^^ ^,jj.^i j^^^^^ coaiforts the dilated pores. 



The Sun diftufcs the early dews, which, if they lay too 

 long_ on plants, would rot rather than rcfrelh them • 

 it alfoprefles them into the nerves, and other analo- 

 gous parts. This influential power operates on the 

 boughs, branches, leaves, and fruit. 

 Th.e Sua aUb qualifies the air, which othcrwife, bv 

 its frigidity, would flop the very courfe of nature, and 



fcems as though it would fuck it up into the glafs •, 

 when indeed the truth of the experiment is, that it is 

 only the outward prefllire, and the inward weaknefs 

 of the air to refifl:, being purified by heat •, for if the 

 fame glafs Ihould be plunged into a bafon of water up 

 to the foot of it, yet the water that is in the bafon 

 would not enter into the glafs, till the air, either hav- 

 ing loft its own ftrength, or racherlnfinuated or incor- 

 porated itfelf in the water, lofes its own ftrength ; fuch 



is the force of air. 



But this may fujfRce concerning what the ancients call 



attraction, which in many cafes is folved by puifion, 

 or the preffure and elaftic powep of the air, rather 

 than by the attractive power of the Sun. 

 Jt is fufficiently proved by ocular demonftration that 

 the vapours of the fea, rivers, lakes, and all the hu- 

 midities of the ground, are drawn up after this 



manner. 



And that heat is an agent in this operation has been 



clearly proved by the experiments of that learned na- 



turalift Dr. Halley, by taking a veflel of water fpur 



inches deep, and kvGn and nine tenths in diameter, 



which being warmed to fuch a degree, as might be 



fuppofed the air might do it, in fome of the hotteft 



months, and letting it iland about two hours time, 



and weighing it, found it had evaporated near half 



an ounce, although there did not appear any reek or 



fmoke, nor did the water feem warm, by putting his 



finger into it; from which it may be concluded, that 



out of that fmall fuperficies of the water, fix ounces 



would be evaporated in the fpace of twenty-four 



hours. 



Upon this fuppofition every ten fquare inches of the 



furface of water yield in vapour, per day, a cube inch 



of water; and each fquare foot, half a wine pint; 



and every fpace of four feet fquare, a gallon j a mile 



indeed it would be difficult to inftance any thino- in 

 the whole circle of botanology, that does not partici- 

 pate of a fliare of this virtual and difiufive <rooi.l 

 From what has been faid we may eafily account for 

 the difference of heat in fummer and winter, viz. from 

 the obliquity of the Sun's rays. This therefore fhould 

 be well confidered in the contrivance of ftoves, to 

 preferve the moft tender exotic plants, Vv^hich ouf^ht 

 to have their glaftes fo fituated, as to receive the S *^ 



direft 



oun s 



upright 



rays m direct lines as great a part of the year as 

 poffible; for which realon the ftoves, which have 



JafTes in front, and {loping glaffes over 

 them, are juftly preferred to any at prefent contrived. 

 And from hence we fee the advantage of makincr the 

 back part and cieling of all grcen-houfes and ftoves 

 as white as poffible, fince it is evident, that the rays 

 of light are hereby reflefted with much greater force, 

 and fo confequently the heat is greatly increafed* 

 which Ihould always be obferved in buildinc^s of this 

 kind. 



From hence alfo we may learn, that countries in the 

 fame latitude may be very different in their heat, ac- 

 cording to their fituation, in refped to the Sun's rays, 

 or according to the nature of the foil in reflefting the 

 rays with a greater or lefs force ; fo that in prefer'ving 

 exotic plants, the heat which they require cannot be 

 exadly determined from the latitude of the places of 

 their growth ; but the fitu^ippn of the places muft alfo 

 fquare, 6914 tuns ; a fquare degree, fuppofe of 69 I ' be confidered, as, whether they grow on hills, moun- 

 Englifh miles, will evaporate ^^ millions of tuns.,v j tamsy or valleys ; and if 90 the fide of hills, which 

 This will account for the Cafpian fea being always at | fide in refpeft to the Sun, withfeveral other obferva- 

 a ftand, and neither wafting nor overflowing ; and 

 alfo for the current faid to fet always in ,at the 

 Streights of Gibraltar, 



always m ,at 

 notwithftanding that thofe 



hy fucfi 



Mediterranean feas receive fo many, and fo confide- 

 rable rivers. ' --: 







This experiment has been carried yet farther by the 

 Oxford Society, who, fuppofing a cubical foot of wa- 

 ter to weigh j6 pounds, and this foot containing 1 728 

 cubic inches, and divided in the 76 pounds, gives 

 half an ounce and 134- grain?, which is the weight of 

 a cubical inch of water 5 therefore the weight of the 

 233 grains 4ttj ^^ Z5 P^^^s of a cubic inch divided 



> - 



by thirty-eight.-- 



-Then the area of a circle, the diameter of which is 7 

 .inches and upwards, is "more than 49 fquare inches, 



'Which if it bedivided by„^ pai'ts of an inch, the 

 quantity of water carried off in vapoursj^ the produdt 

 will be 



experiment. This is a plain proof of what a great 

 quantity of water may bq_ thus carried off, in great 

 dimenfions of water, even enopgh tpTupply all rains, 



&c. 



in foreign countries, i';..^ \;- 



I Ihall here add a'^table of jtKe ihadow of the Sun at 

 the feveral feafons of the year, which was communi- 

 cated to me by Mr. Timodiy Sheldrach of Norwich, 

 by which a perfon may more readily fee what effeft 

 walls, buildings, trees, &c. have, in ftiading the ground 

 to feveral diftances, according as the Sun is more or 

 lefs elevated above the horizon ; as alfo how great 

 the fhade will be in the green-houfes, as the p iersare 

 in breadth, or the wall in front is in height below the 

 falhes. * 



_3 



or 



parts of an inch, wafted in that 



r^ -.^- 



t . 



-• 



dews, 



-But the Syn, befides this, has a diffufive power (not 

 .to dwell on the light it conveys to thefe fublunary 

 - regions) without which the whole race pf mankind 

 muft wander and grovel in the dark, for by its genial 

 and chearful rays it exhilarates the vegetable part of 

 the creation, and makes' natures herfelf to fmile. 

 -It has an influence upon deep grounds by warming 

 and chearing the pores of the earth, when diluted and 

 fodden by too much wet, and puts the emulgent fi- 

 bres of plants upon feeking their food. 

 It helps the furface of the ground by attrafting or 

 difpelling the vapours, which would otherwife make 

 it noxious \ but more particularly it warms and heats 

 the ground, and by its powerful influence contributes 

 to diffolve the latent fait, and prepares them for being 

 fucked in'by the fibres of the plants, which, by the 

 fame genial force,- are put in adion to feek out for 

 . their food, -y^ 



O an 



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3c 

 40 



60 



80 



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 40 



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 30 



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 40 



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Lat. 5 1 



°3o' 



The length of the Sha- 

 dow of a column of 

 five feet high at the 

 time the fun enters 

 every fign. 





in 





a 



5 feet 



1 



2I 







25 





a n 



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The firft three tables fhew the length of fhadows in 

 the fummer and winter folftice, and in the vernal and 

 autumnal equinoxes. Suppofe a mountain, column, 

 or other body, whofe perpendicular height is one de- 



The length of the Ihadow from any thing of 



gree. 



-:.V 



*•* •"——_. ■• 



*; 



that altitude is here fliewn in every degree of latitude; 

 at the above-rmentioned times, in degrees and mi- 

 nutes, and where a Iborter meafure than a mile is 



The fourth table 



required, it is flievvn in feconds. 



is calculated for the latitude of 51° 30', 



■ This fourth table fhews 



which is 



-* 





s 



pretty near that of London, ■ 

 the length of the fliado\1r,made by any perpendicu- 



^ . ' lar 



