lights which is to.be found in the fecond' part of ;the Hiftoire de
1’ Academic. This hypothefis requires the following concurrence
of there-mufl:" be vapours in the.'upper- regions.’of
the air; next, fome clouds of that fort, and thefe at a vaft height,
and in the north; arid they muft npt only emit vapours, but be,
illuminated and irradiated by the fan, when it is invifible to us;
and of; confequence, the fun - muft be vifible to us at fuch i time,
if we flood as far above die horizon as the faid clouds. g And
laftly, there muft be a north-wind in the. fame upper region of
the air. to fet it in. motion;, and to give a difpofition to the'.ffy
gures, which fofuddchly change ftheif .appearance. It is. ppfliblo,
that the experience of pofterity may fuggeft fomething more
probable.
The author’s If I may he allowed, onexpeiSted, to add any’opinion 6£.my
cefning die” own on this problematical fubjeth;. it may perhaps be not more
north haht than what hath been already alleged, if we admit1,
that the original eaufe of the north-light lies'in the
the etherial a ir;, and, ’ confequendy^ .thatjitthas gxif|:ednat,.,all
times, and in all places,' they, not yifible to^jus, without ^ eomcux-
fence of fuch concurrent circumftances anej, qmrftures,.. as :I mall
here exhibit. It is not above twenty yfaj^'fince the eletftrfcal
experiments have become ‘ggneralfy .known, and^aSs ^they have
ex ited .the,attention of-all lovers of natural knowlege,. they have
likewife filled, them with hopes, that t^^difcov%wyvould_Ppen a
way to the folution of many more myfteries in nature. I flatter
bnfjhe flrfl: exneriment-fof
any. importance, which has occurred to-me,, relates'to. this very
point of deducing the north-light ftom-thg, electrical, jfee^le, and
fubtile fire of the,air, which by mea®.scof ^hqfi^ore rapid cirguin.T
volution of the globe on its poles, on axis, * excites a' more vehement
concuflion, or agitation, in the air'of the-northern: climates,
aadQriius dhpMys theeleriricity oftheethej-eal air. rqofl: confpi-
cuoufly in thofe parts. .1 was flrfl; led into thefe |^e<!|i©ns;fpmeT
time fince by a ’converfation with a friend of mine, a, very ingenious
naturalift, who fheWed me a remarkable paflage in -the
Eibliotheque Britannique, -Tom. xxi; P. ij. pag. 336. where,
among o|her extra&s.dfom the Englifh Philofophical .Tranfac-
tions, is part of a piece of M. Defaguliers, intitled, A Diflerta-
. 2 ’ - , tion
N AW cR c A E H TSyTTO,!^ of WXhT. 9*
tipm'.CQnfiCJSling iTh® feopScof; hisf demonftrafinns. is ;
V&e. tp.fhqw-.fcbe mue-esufe. fth& afeeqt c£'
and; tl|ft poWfSf; by which; if remain^. ^paring in the-1
ai^,. which- isf,4tv,allL tjfftes; auch lighter .than w^teis But as the
inye^igatäß®: QßO truth, often* ptove&H-mrQdifel&jy to-another,
fq^in, t-hjis paflagg; the, waiter feems. to-diiccSb us to a dearerinftgfo-’
iÄtP>|tl|f;^^L and' mature -®fi th& north-light1. | P fliafl1 therefbreiqfefc
;®' TO&eh^-bij thgihpafl&go-herej as relates to our purpofe.
Iß; ©rdfcr t®i apprehend' hife-meaniF!^^i^^|feA'vift< recollect with the^
leasneric, writer, that'Mr-. ©u Fay-a obfervatiqn, “ -that there are
iwo-fi^it-i of eledtrkity,” h pi in ed-by obfervätions'and experiments';^
a^adi that the- efedtrifcaf- bodies of ä intfeolls“, - , y mn tüälly
repel; @me-another; wbilft tfoty attiaft thofe of a ’iclmtru ^mpwHpM
ty>. alfc. that- thofe qf a refinous efefeicity repel one' ariöther, 'änef
attnari thofe of a vfeeous eledfcridty.
% I iuppofe, fey« Dr. Defegulfers, pätdfcfes''jqf4 pure air,to *bd
elerinc bodies always m a flata o|? el'edtricily, and that jdtteqiis-
. eledmichy^
ifl; Beoaufe particles ©f äh rep^l '
irg, as has been dfedmood from experiments äml' ofe^ryatibns. ?
^dly, Becaufe when the air- is dry, - the ‘gfafe-tube rubjb’d1 (8r
e@ly warmed) throws-out- itaeffluvik^ which the air drives’back’
to fhe- tube-;, from whence,;theydart out ^ d 5'fe> move
backwards and forwards with a vibratory motion, which continues,
their efedhrieity.,
: 3.dly, made eie£tric. by the tube, and
. datted fem» it, keeps- its elelfriclty^a l^ - ' l | i i lT h <%dry'air;
whereas when the air- is moift, the mqift particles,1 which arh non-
fle#lics, flmting’im the air, and 'being a to n ed
adhere to it; and foon make -it 1-ofe 'its efe&ricity; which -alfo
happens- even t6 the tub© in a
From this eonflder-ation it will be eafy to account for a fämöus
experiment of the.late Mr. Haukfbee, which is;thi^V'“
Hawing pump’d out aäl the air from a gfaß-gfobe, hq caus’d it
to turn 0p its axis, ydry fwiftly bynm'IShs of a rope with a,'wheel
and pulley; then rubbing the- glafs with his" hand during its mo-
fW) there appear’d a great deal of light öfapurple colqur within
the globe, without any light oräftraäion bbfery’d on the ouiiTide-
of the glafij, which is obferv’d when the air has not been punip’d
Part I. D :?i out.