Observations of the Transit of Venus Over the Sun, Made at the Round Tower in WindsorCastle, June 3, 1769. By Daniel Harris, Master of the Royal Mathematical School in Christ'sHospital, and F. R. S. In a Letter to the Reverend Nevil Maskelyne, B. D. F. R. S. andAstronomer RoyalAuthor(s): Daniel HarrisSource: Philosophical Transactions (1683-1775), Vol. 59 (1769), pp. 422-431Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/105858 .

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r 422 J

LX. Obferuatiors of the tranft of Verlus oser the Sun, nsade at the Rxnd lJoqwer in Windfior CaRleX June 3, T 769. By Daniel Harris, MWer of the Royal M- zbematical School gn ChriR's Hofpital, and F.R. S. In a Leter to the Rsererd Nevil MaRelyne, B. D. F. R.S. snK XJ?roromer Royal.

SI R,

Read Dec. 2Isr H AV E taken the liberty to fend you 769* I my obServations on the tranfi1t of

Venus, as likewife thoSe made for aScertaining the going of the cloclr; all which I lhould harre done laR JllneX when I fent the times of the contadrs, ta the end that they might, if you thought them wor- thy, have been communicated to the Royal Society -through your llands ; but, waitillg for an opportunity of uf1ng your tranfat-inRrument, in order to aScertain the longitude of Witldfor, which you was fo obliging to lend me for tha$ perpofe, prevented; and am forry Rill to fay, that I have not once been able to make uSe of itf on account of the badneEs of the weather at tile feveral titnes I took it down with meforthatpurpofe. Hosvever, oehermethQdshave

been

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[ 4239 ] been made uSe of, and no pains fpared for aScertain ing that rllaterial point, in ssrhicla I hope I have fuc- ceeded, as well as in rnaking the other neceSary ob- fervations; and Whall be happy if they rneet with your approbations and in any way and to affilR in determining the grand point in quefRion.

Aly f1tuation for obServing elle tranGt, and making the previous obServationsX was extremely advantage- ous; all of which were ulade witllin hearing of the clock, which was a good regulator, fixed up in the .Round Tower a fortnight before, by p:ermifl5lon of the Governor, his Grace the Duke of Molltagu--; who was fiQ obliging, UpOll Sy worthy friend Captain Alexander Schomberg's application to hinl, byletter, in both our names, immediately to give his conSent, with Ilrift orders to his Servants to take care that we were not di(turbed irl making our obServations, par- ticularly on the day of the trarlfit; whicll orders were moR pundually olteyed; nobody being ad- mitted into the Round Tower on that day but our- ISelves, and tsro others, as aElRants to watch the clock; vis. the Reverend Dodor Bollock Canon of Windfor, and -the Reverend Mr. James Townley, Head-maRer of Merchant Taylors School; both gexltlemen acquainted with the nature and. uSe of aRrotromical obServations-.

The regularr was fixed truely perpendisulur, and well faftened to the wall and floor of elle room where the tranf1t was to be obferveda and obServations tnade on its rate of goiazg fa feveral preceding days, both by Captain Schomberg, an officer, well ac- quainted with aRrononzical obServations, and my- Iclf by which vwe fotlnd tllAt it loR at the rate of

tssenty

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s ^

424 twellty [ecollds per day nearly. The greslteft part of the altitudes taken for that purpoSe) wit}) a booul Hadley's qadrant, in a ucerof treacle allul sratelX conrered witll your glafs roof, whell neceflary, tcs Screen it from the wind, whicll I fbund to be of great ufie, are herewith inclofed, with their cor- refponding times, &c which have all been com- pared Separately, in conlpliallce with your requelifi both by Captain Schomberg and myfeif; and which 1 hope svill be fbund t be fatisidlory.

As to ehe longitude of Vfindior Caftle Som GreenwichX svllich has fo long engaged my atten- tion, though I have not had an opportunity of aS- certaining it with your tranfit-inItrlamentf by the me thod of diffierences of asimuths, which I have long wanted to do, yet, nc)twithRanding, by a mean of Several bearings of St. Paul's, taken fronl the corner of the terras, near the dial, with a good theodolite, and fbund to be N. 82° 3o' from the true Incridian, and the diSrence of latltude between thae cathedral and Windfor Calile 2i geEraphical mil", think it may be very nearly determined; and in the fbllow- ing rnanner.

The latitude of St Paul'sX or, which i8 the fame thing, of the Royal Mathematical School in Chriil's HoMpital, by the mean of a great number of obEerva- tions, I make eo be5X°3o'4N.andbyameanof IEveral double altitudes of the Sun, taken in a faucer of treacle and water, Screened fFom the wind, I find the latitudc of Windfor Caitle t be 51° 28'* NX the ditErence of latitude therefUre between thofe two places is 20 rograKical miles; with whichs and the bearing of Se Paul's fFom the Caflcle N. 8:° 3o' E.

(variation

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[425 ] variation zoi degrees allowed for), I make the dif- ference of longitude between them (by Mercator) to be 3oi miles, wllich is equal to 2t 2/ of time . and recolleEting your mentioning to me Dury and Bells adrual Survey of London and its enrirons for 3o miles3 as of fome uSe for the purpoSe, I have looRed ourer it, and find by that, that the direEt diIlace be- tween WindSor Ca(lle and 2)t. Paul's, London, is 22 Ilatute or meafured miles: and by another Survey of the fame kinds done by Kitchen, I find the diRance between thofe two places to be very nearly the fame. Therefore, with this diRance of 22 miles, equal tV I 9 geographical ones, and the difirence of latitude, by ohferaration, between tlle two places 2 I miles, I find the departure to be I8,8 miles, which gives 30,2 miles of longitude, equal to 2t It of time, agreeing within a fecond to the former method

The difference of longitude or difference of meri- dians? therefore, between the Round Tower Wind- for Catile, and St. Paul's, LondonX I think I may Yenture to put at 302 tniles or 2/ 2tr Of time; thou« I am per(iJaded, if any thing, it is rather more than lefs; to which if we add the diffErence of longitude in time between St. Paul's and Green- wick? which is 22Z'T, ie will give 2/ 24"T of tinze for the diffierence of Iongitude betwec-n the Round Tower at Windfor CaRle, and the Royal ObServatory at Greenwich.

I cannot help obServing, that the only inconvenient circumaatzce, during the time of obferving the tranfitt was the wind; which, blowing rather hard, and di- reEtly into th.e teleScope, together with the fmallneSs

VOL. LIX. I i i Of

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-[ 426 ] of the Sun's altatude at th:at timt made the limb §o very ill defined and undulating, that it is-poi1blc there may be an error of five or fix iEconds, at ieafi, in the time of the external conta&: being anxiouss therefore, of having the internal contadc as exadc as po}ble, I changed the magnifying power of my telefcope from that of tz5 timesX recommended by yourfielf, to that of 55 times, the leai} of all) which fucceeded beyond expeEtation; for by- this means that undulati}zg motion of the Sun's limb was greatly reduced, though not entirely ta-ken away, appearing mtlch better defined than before, as did likewife that of the Planet Venus; infomuch tht the error, if any, in the time of the internal contaft, by which I mean the completion of the thread of Jight formed by tlle Sun's circumferel}ce, cannot exceed three Seconds. The obServing of the two contafts with fO different magnifying powers as that of I25 times and that of 55 times, mu{t occa fon fome difference in the times, and duration-be- tween the two contadrs, to what they vfould have been, had they both been obServed with the fame magnifying power ; which is to be allowed for.

Venus appeared remarkably protuberant on her upper limb, both before and at the time of her in- ternal corltaft, which went gradually o£ fioon after, bwt did noe though I earneRly attended to it, ob ferve any thing like an atmorphere about her.

Be pleafed, Sir, to accept of my bell tlsanks for the uSe of your glaSs roof and tranfit-inLtrume}t, as likewife for your very obliging and uSeful communicatsons, at different timesX on the prefene

fubjeXts

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[ 427 ] fubjedt, which I ihall always have tlle moR gtateful fenfe of; and am, with real efl:eem,

S I R} Your much obliged, and moll obedient, humble fervantF

Boyal Bfatbematical Schonl, D 1 H tn ChriRs Hofpital, anle arrl8^ Dec. 21, I769.

Times of the contaEts of Vcnus with the Sun, as obfierved fronv the Round Tower, in WindCor CaRle, by permiffilon of his Grace the Duke of Montagu, June 3, I 769.

Latitude 5 ° 28't NB and longitude 2t 24" 2 itl time, WX frosn the Royal ObServatory at (;reenwich.

By the clock. Mean time. h / tt b t {t

TheexternalcontaAof Venus }\7 4 30 7 o6 I4 p z

w;ith the Sun, The internal contaXt at 7 ^2 38 7 24 22

Duration between the contaAs, ths clock beingl o 8 o8 I' 44tr tOO flow for mean time, J

§ Venus's diameter meafured 3 different times o 590

Ghords meafiured parallel to the equator. Venus's weRern limb from the Sun's eafiernl

Iimb, at 7h 46t o4" mean eime | 3 4z Venus's eaflern limb from the SuSs wellernl 6

limb, At 7h 47 04" meantime 1 5 I

NeareR di0ance of Venus's }ower limb froml the Sun's limb, at 8h ot SS/t, the lall of her J 2 49

The Sunss horizontal diameter (at 7h 3°t) 3I 42

Note, Thefe obfienrations were made with a good regulato; made by Binning, of WindCor; an 8 incb sefledcor, made by the late ingenious Mr. Short, and a double objed glaEs micro- nleter, made by Dollond.

* The very fame that I madc it at the tranfit, x7Cz. Arz I i i 2

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[ 428 ] An accollrxt of the methods ufed to afcertain the going of a

clock, fixEd up in the Round Tower at WindSor C;lflle, in latitude 51° 28': N. from the 30th of May to the 3d of June following, 1769.

.-By a mcan of three double altitudes of the Sun's center, the limb not being well defined, taken

! May 3o with a good Hadley's quadrant, made by Adams, < in a faucer o¢treac'e andwater, foplaced within

h tbe room as- not to be diRurbed by the svind, af- at 44 p. n1. ter having svorked each Separately, I found the

1 clock to be 3' I8t' tOO nOw for the Sun, and t o' 25't too nOw for mean time. fBy a mean of four double altitudes,] s , | of the Sun's upper limb, after being t

V NIay 31<1 worked fieparatety, found theclock too ( ° 4° at84a. m. | ,nOw for mean time J

l And by a mean of 3 correfponding alti- l o 48 titudes the fame afternoon J

% June I J*By a mean of 4altitudes, worked fepa l I oo at 52 p. m. t rately, too nOw - J

rBy g ditBerent altitudes of the Sun's up- z I per limb, all worked fieparately and I 16t

2 June 2 2 takin$ the mean, found the clock eQo X at 8.+ a. m. llow

And, by aS mean of 3 correrponding alti- \ x X i tudes, the fame day J 7 r By the mean of t-wo altitudes only; 5

T2 June 3 1 the weather not permittil)g more, l 2^ at8wa.m. ) made the clock too nOw for mean 0 I

t time J (The fame afternoon the weather beingo

Ditto J extremely fine, by 4 more double al- t t * 5 titudes ofthe Suns upper limb, vvork- g I 42

at44 pe m 1 ed fEparately, and a mean takell, houiid l < the clock too now for mean time J

* Wound up the clock juflc before thefe altitudes were taken, which might aSeA it fiomething, although a regulator

By

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l 42g, By 4 more double altitudes an hour after,)

[ the weather being exceeditly fine) ttlo' t

b June 3 J windy, whicb obliged me to ufe the g} rs !>

at sbas p m. roof, by working all of them fing!ys f - and takint, a means made the clock tocw |

i Slow for mean time J

J

I 43 __

By all which it appears, that the clock loll of mean time, from the 30th of May to thc 3d of June, inclufive, at the rate of 19i feconds per day; and by the lall fet of obLervations, at the time of the tranGt, X fiecotld per hour.

.

Some of the foregoing double altitudes, with their correfiponding tinles as {hewn by the clock, and the refults, are here fubioined.

t June R The weabther verg fine.

Double alt. t 's u. 1. Cl. too flov¢.

O , , tJ

Times by clock. h t tt

At 8

-

-

-

-

-

a. m. 8t o62 8 t 582 83 30 g5 I 9 86 232 87 16 89 3s Ditto center I:)° lower limb

3 4I =

3 43 W 3 49 @ 3 39 S . 3 49 <;.: 3 47 O 3 5I

3 44 o_s

3 SI C,)

9)- 4I4

3 46 -2 294

I 164

25

33- 4o 43 46 54 56 58

ss 45 47 3 35 37 35 3o o7

By the mean of all, clowk too llow for the Sun Equation of time

Clock too flow for men time

Carrew

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Correlwponling altitudes, taken the- fame day.

Times by cl. Dou. alt. h f t! O f

At 8 8 8

5 I8 8 32

It 44

74 50 liptlimb - 75 540 76 s3

h t rs t tt

I t52 ° 2 g I 2a eS*

I 251 Q ¢ a

3)3 5I

3 47 3 44 3 4o

44 OI

38

By a mean of the three, cl. too nOvv for m. time X X t

15 June 3 The weather try cloudy, and likely to rain.

D.alt. O t

78 I6 Up. limb. 79 02 ditto.

h t tt

.At 8 JS 47 a. m 8 I8 I7

3 49 3 43

__

3 46 2 .2o

x 26

o Q =

3 u3 _ o,=

Cl too flow for the Sun, by the mean

Equation of time

Clock too llow br meaa time.

AtJain, At 4 1s 38 pm-

I4 2I - x6 Sx _ ,X9 01

4 02 3 SI

4 ot 4 o3

4) IS 57

3 59i 2 I7

I 42 , ,

67 3xt upzlimb 66 44 65 54 65 I4

By the mean, clock too flow for the Sun E:quation of time

Clock tOO nOw for mean time

Again,

[ 43° ]

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[ 43I ]

Double alt. O ,

- 48 56 48 o82 47 28 46 48

Again, t ll

up. limb. 4 Ol 4 Ol 3 59 3 57

_

4) I 5 58

3 S9t - -2 16

*

il 43 r

At5 1t - I4 _ I6 -18

Clock too Jlow for £he

oun

35 5 I9 27

Clock too llow for the Sun Equation of time

Glock too iw for mean time

LxXr ObA¢r

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