An Account of the Remarkable Cold Observed at Glasgow, in the Month of January, 1768; ina Letter from Mr. Alexander Wilson, Professor of Astronomy at Glasgow, to the Rev. Mr.Nevil Maskeline, B. D. F. R. S. and Astronomer RoyalAuthor(s): Alexander WilsonSource: Philosophical Transactions (1683-1775), Vol. 61 (1771), pp. 326-331Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/106108 .

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[ 326 ]

XXXVII1. Sn Sccovrt of the rexnarkable Cold obyre> vgd at Glafgor, in the Morth of JnUaly9 I768; in a Lezter fram . Alexallder VVilSon, Profe%5or of A>Cronc>zy at GlaEgow, to tbe Rev. Mr. Nevil Maike- line, B. D. F. R. S. and v4J?ronomcr Royal.

Reverend -SIR,

CollegeX Glaeow, May 29, I 7 7 I .

Read Nov. 7, lr tAVING of late had fome leifule I7tI. n time, I have made out fi-otn mv

minutes, a detail of the remarkable cold which pre- vailed helhe in the month of January, I768; the intenflty of which being fo extraordinary for this climate, an account of it may perhaps be thougllt worthy of a place in the PhiloSophical TranlC- tions.

NVhilI} in bed, on funday morning, January 3, 176S, about 8 o'clockX it felt fomehow uozufiually cold. A little while after, OIl reaching GUt for a decanter uZhich I had placed near nae the preceding

nigllt,

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[ 327 ] night, with fome water in it, I was furprixed to find the furface of the water froren over, the like not having happened before in that place. Upon this, I deflred my fon to try the cold by a thernzome- ter, as I itnagined it behoosred to be very intenfe.- The experiment vstas foon after made, by expo§1ng a thermometer at a high North stindow) and free from t}ze sralls of the houSe; in: which f1tuation it had not remained fbr a quarter of an hour, when we fotlnd the mercury-had fallen fo lozr as to 5 deg. of Fahrelllleitys fcale.

Although I had expeEted a great degree of cold, yet I wras not quite prepared for fo extraordinary a re- port as that vuhich the thermometer now gave me My doubts weres however, foon Settled, by examin- ing matters with more attention) and by finding the fir thermometer verified by nly Randard one, which was now hung out befilde it.

Being tilus fatjsfied that there >as no fallacy in this preliminary obServation, it natural]y occurred, that the cold, however intenfe it now was, might have been mllcll nzore fO at fome earlier hour of the morning. But how to afcertain this, and to recover the loI} ob- fervation, was the difficulty. In the eagerneEs of our difappointed curioilty, we were diEpofed to mag- nify tlzis golden opportunity, which had now efcaped us, and to refleEt upon it with regret, wllen luckily a little invention llelped us olxt. A notion lugge{le(;l itSelfs thatS if we srent very warily to work, we might perhaps furprize thofe imagined colds Rill lulking under the furface of the Enow, which at that tinze lay thick upon tlle grotJndv

I need-

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[328 ] T lleed nc,t mention upon what princip]es of tlle

lleatil)g and cooling of bodies this exped:tation was fotlllded, as tlley will readily occur of; tIzemSelves. The fact was, that I itnmediately repaired to the fields, and lollblatout a low place, upon which the iUll had not then rifen; hWre I laid the thermometel in the filovt, almoll upon the vely furface, when pre- *ently the mercury funk from +6 (lPg. to _ 2 deg which therti7ore I concluded to have been pretty slcarly the coldeI} temperature of the air over sight.

The next thing was7 to make regular obServations with the therlllometer, fO long as the cold promifed tocontinue remarkable The inRrument was hung upon a pole near to the obServatory, and to the wind ward of it, care having -been alro taken to keep it under a proper ihade, -fo long as the fun {hone out.

Regiyier of the Tybermometer, kept az zbe M'Farlane obfieruatory, of the college of Glalgow, on fiunday yanuary 3, and alonfilay 7unu- ary4> I768.

Sunday IO o'clock + 5 deg. mOrnlNg I I 7

IZ 9 The temperature of the fnow afiterno¢n I IO on funday morning, at about ten

2 I I inches below ti furface was near 3 92 to 3o deg 32 62 4 3z 41 2

2 20

6 xi 62 °2

7 - I 72 o

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s - oD

8 - I-

9 - 2 9E _ I

1o- - z

IQx - 2

Z1 - 2

I:Ii - X t Some appearance;of clouds in the - o j S.E.

I22 - O I

Manday x - I

rsornlng n -- o zi t 3 1 Clouds gathering, ancJfome wind

: 3 6 j from E. 3 7

2 Quite overcaR, wind E 42 IO Dieto 5 1 2 Ditto

I-t was olzrerval)leX that after fun fetting, the atmof pllere had a tendency for.letitnes to turn a little foggy, and again quickly to clear up, balancing, as it were, betSwixt theSe two different {lates. It is yvorthy ol: notice, that the minute-variations of the thermometer,; as Set down irl the above rWt,iIler, feemed to depend upon theSe differen-t conItitutic)ns of the air; the snercllry always riI1ng in tlie thermome*er a fmall matter, when the mi{linefs catne on, and v(e serJv.

Jn thc intervals of oblorvations, we made fome other experiments, which the preitlt intenfity of tlle fro Slggelled; particularly one r.eating to tlle evapordtioIl

of ice, wlzxch WdS tried in the following tl3annerO I took a Square refleEtilzg tnetal belonging to my own twe fioot tele{copv, a-rd expoSetl it on the ballvRrade d thfi obServatory, tI11 it lad acquiied the tCE)pCt'-

tbr& Of the placeJ svlaich w;s tllen at Q dcg. attel it VOL. I>XI. U U VY&S

t 329 ]

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[ 33° ] was thus cooled, I breathed on !it repeatedlgf, till it$ polifhed furfaee was coszered over with an inctllllation of ice or frozen vapour, of a vety palpable thicknefs n this condition the fpecularn sras replaced xn its for mer fituationX having its incruRed furface expofcd to the Ilill open air; when, ill a little time, we fotlnd t]e froscn pellIcle begining to difappear at the outer edge, all around, leavillg the metal qllite clearw Gradually more and more of the fipeculum was bared irl a regular progrefl:lon, frotn the circumEeretlce tow wards tlle-centre; and at laXit, in aboalt 50 minutes, tlle wlaole furface had parted with ies ice Tlais ex- periment was repeated wllen the {peculum sras de fended from the open air, by a large thin box, svitIl a c}oth oster it, The ea3erlt tlxrned out the falne as before, only it requred longer time.

This progrefs of the evaporation frotn the outward parts towards the centre of tlle hpeculum, was likely owing to the original plate of ice beiIlg thickell to- wards the cetlters a circumftance which might alife from tbe tazaureer of fixing it at fir{t breathing on it. Or perhaps it may be imputed to fone more curious saufe, atad may be fonze eSeEt of ehe repulGere force belolzging to the polithed furface; but this point we did tzot fufiiciently e-xamine into, by a due repeLitio of experitMents. I may ju(t meration, vlzat, partly with a wiew to this matter, we expofed as above, a fet of ;bodies, having their furfaces of different deP grees af poliSh, and as equally covered with froxon xnoitRu.re as sbre could judge. Tlle refult of which expsriments feemed to favc:ur the idea of the ice being lef$ attached to tlue more polithed furface than to the coarfer, This appeared partis:ularly in the

cafe

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[ 33t ] cafe Qf a comparifol) made betwixt the fpeculum above-mentioned} arld the brafs end or cover of the fanle telekope; for the ice was found llill to cleave to its furface a good while afier the fpeculum was entirely cleared. TheSe imperfiA experiments ar¢ only mentioned ly the bye} and tllay perhaps ferve as hints to others, who may be d;fipofed to proSecute this pa-rt of nat:lral pllilofophy. - -

Sotne partictllar reafons have occurred, which will lVinder me from tranftnitting to you the paper on the iSolar fpotsfi till fiQme time t}ext winter, by w?hich flme I Qlall have finiIMed. every thing I have to fay on that fubjedc Wilhing to hear from you at your leifure, I ever atns wi mllch refipedt,

Reverend Sir

Your tz30ft ob-edient fervantfi

Alexartder Wilin7

Profdor of ARmnomy at Glafgow,

trul X hce;vg

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