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Full text of "An Account of an Observation of the Transit of Venus, Made at Isle Coudre Near Quebec. In a Letter to the Reverend Nevil Maskelyne, Astronomer Royal, from Mr. Thomas Wright, Deputy Surveyor of the Northern District of America"

[ 273 ] 



XXXVII. An Account of an Ohfervation 
of the Iranft of Venus, made at Iflc 
Coudre near Quebec. In a Letter to 
the Reverend Nevil Mafkelyne, Afironomer 
Royals from Mr. Thomas Wright, De- 
puty Surveyor of the Northern DiJiriB of 
America. 



Quebec, June 15, 1769, 



S I R< 



I 



thick weather) ; but, however, 1 had the good for- 
tune to reach the ifland of Coudre, where I landed, 
with all my apparatus, the 30th of May j and took 
up my abode at a houfe well fituated, in every reipecfl, 
for my purpofe. The next morning I had a car- 
penter, who fixed my clock, very firm and perpen- 
dicular, againft a beam of the houfe. I immediately 
fet it a-going by my watch, which had not been fet 
to true time for almoft a fortnight \ but, however, I 
doubt not but that the following obfervations of cor- 
refponding altitudes will fliew exactly the time, as 
Vol. LIX. N n alfo 



[ 2 74 ] 

alfo the regular rate of going of the clock, which I 
did not venture to adjuf!, my time being fhort. 

As it is likely I may flay here fome time, and all 
next winter, I fliall endeavour to make fuch obfer- 
vations as may be ufeful in further fettling the lon- 
gitude here. 

Captain Holland obferved the external contad, 
but not the internal, being prevented by clouds. He 
has fent them to you by this opportunity. 

I am, 

Si R, 
Your moft obedient,. 

humble fervant,, 

Tho. Wright. 



Corre- 



[ 2 75 3 



Correfponding double altitudes of the Sun's lower 
limb, taken with a brafs fextant, by reflexion, from 
a faucer of oil, fo placed as not to be the kaft 
difturbed with wind. 



Thurfday, June i, on the north- weft fide of the 
ifland of Coudre, in latitude 47 16' 30", determined 
by feveral obfervations of two altitudes, with the in- 
terval of time fhewn by the time-piece. 



Morning, June I, Pou. alt. Afternoon, Compared Separately give 

h f ff of h t ft h t rt 

At 8 29 45 7$ 38 

8 32 52 70 42 

8 35 5° 77 43 

8 38 31 78 38 

8 4° S3 79 * 6 

8 43 34 80 20 



At 4 8 54 


22 19 19 


4 5 37 


12 19 14 


4 * 39 


12 19 14 


400 


12 19 l£ 


3 57 2 4 


12 19 08 


3 5S 


12 19 17 



8 36 54 Mean 4 i 36 Mean 12 19 i£ Mean 

16 01 36 Add 12 



7 24 42 Interval 16 01 36 



HmMaaaMOM 



3 42 21 Half Interval 

8 36 54 Time in the morn. 



12 19 15 
-00 00 06 Equat. of correfponding alt. 



12 19 09 Time jhewn by clock at apparent noon 
+ 2 3 J Equation of time— from apparent noon 



12 21 44 Clock too faft for mean time 



*■»■ 



N n s Friday, 



[ 276 ] 

Friday, June 2. 



Morning, Dou. alt. low* ltznb. Afternoon. Compared feparatefy, 

h / // o / h / ft h ' tf 

At 8 54 28 84 19 3 42 20 12 18 24, 

8 56 40 85 00 3 40 12 13 18 26 

8 58 50 85 45 3 38 02 12 18 26 

9 2 34 87 00 3 34 13 I2 18 24 

9 4 2 8 7 *7 3 32 45 I* 18 24 

■ " " ■ ■ ■ ■ » . 

8 59 19 Mean 3 $j 30 Mean 

15 37 3° *z 

6 38 it Interval 1 5 37 30 



3 ! 9 5 1 Half Interval 
8 59 19 



1 *■ tS 24I 

— 4 Equat. of correfponding altitudes 

1 2 18 2of Clock too fall for apparent time 

4-2 26 Equation of time — from apparent 

12 20 46I Clock too fail for mean time 

21 44 Clock too fall at noon of June s 

o 57! Clock has lofl in 24 hours 



Saturday, June 3, the morning cloudy, no altitudes 

taken. 



n 



At 2 49 22 by the clock, I happened to take my eye off from the very 

point where I afterwards found the external contact 
happened, imagining I faw it fomething more to 
weftward ; but, finding my mifteke, I returned to the 
former point, where I found Venus hadmade a very fmall 

% 50 25 impreflion at 2 h 50' 25", as is fet down in the margin. 

3 07 48 time when Venus appeared compleatly round to the eye, 
and to appearance rather detached, and- joined by. a 
fmall dark thread or figament, which prevented the 
rays of light from appearing. 

3 q8 19 time when the rays of light juft appeared, at the internal 
contact 

The 



[ 277 ] 

The following is the above times, as fhewn by the 
clock, reduced to apparent time, by allowing a 
proportion of 57 feconds, its regular lofing in 24 
hours 5 as appears by the preceding and the fol- 
lowing correfponding altitudes. 



% i it t n h / f 




2 49 22 iy 32=2 31 £0 apparent time of the 1 ft obfervation. 

2 5° 2 S 1 7 3 2 =2 32 5.3 apparent time of the 2d obfervation. 

3 7 48 17 31—2 50 17 ap. time of i ft obf. of internal con ta&. 

3 8 19—17 31=12 50 48 ap. time of zd obf. of internal contaft. 

The appearance of Venus at the in- 
ternal contadt, when joined by a fmall 
thread to the Sun's limb ; as alfo the 
fpots of the Sun, as obferved at the 
time of the tranfit r and two days be- 
fore. 

By means of two oblong fmoaked glaffes with dif- 
ferent {hades, made to Aide in a groove fixed to my 
telefcope, the phenomenon appeared very difHnd: 
and pleafircg to the eye, notwithstanding the weather 
was a little hazy, and very much fo, near the horizon. 
The thermometer flood at 74 degrees at the time of 
obfervation, and the weather was remarkably clofe 
and fultry two days before, and quite calm till an 
hour before the tranfit happened, when it began to 
blow very frefh. June 4, the weather continued 
much the fame, and about g h 30' in the evening, we 
had afhock of an earthquake, which lafted about four 
feconds, and alarmed all the inhabitants of the ifland. 

The weather, at the time of the tranfit, was not 
clear enough to obferve the leaft appearance of an at- 
mofphere round the planet, fuppofing there really 
had been one. 

Saturday 



[ 278 ] 

Saturday, June 3i correfponding double altitudes of 
the Sun's lower limb for midnight, taken in a 
faucer of oil. 



June 3, 
h 

t 4 
4 
4 
4 
4 


, Aft-i 

4 
6 

8 

10 

12 

8 

2 5 


moon* 
n 

2 5 

43 

34 
42 

C2 

39 

24 


Altitude* 
' 

76 $8 
jo 10 

7£ 33 

74 5° 
74 08 

Mean 

Interval 
Half Interval 


Morn, June 4* 

h / // 

8 29 41 
8 2J 21 

8 25 26 
8 23 20 
8 21 11 


Compared fepari 
h / " 

12 17 03 
12 17 02 

12 17 
12 17 or 
12 17 02 


4 

20 


8 25 24 
12 


Mean 


16 
8 


16 
08 


45 

22* 


20 25 24 


■* 



4 ° 8 39 



12 17 o 1 1 Time of midnight as fliewn by clock 
+ 9 Equat. of correfponding altitudes 

12 17 i of Clock too faft for apparent time of midnight 
+ 2 11 Equation of time — from apparent 

12 19 2 1 § Clock too faft for mean time 
20 47 Clock too faft, June 2, at noon 

■»' ■ 1 ■ 

1 25I Clock has loft in 36 hours 

£7! Clock loft in 24 hours by the preceding obfervations 



28| Clock loft in 12 hours by the prefent obfervatioc* 
which is very near at the fame rate. 



Double altitudes, taken with a fextant, in a faucer of 
oil, for finding thelat. of the place of obfervation. 

June 4, morn. Alt. © J. limb. Afternoon. Doub. alt. Q 1. limb, 
h / ft of h t it o / 

At 10 34 7 115 12 2 1 50 114 36^ There is 3 1 to be 

10 36 44 n6 00 2 4 32 113 46 I fubtrafted from the 

10 37 40 116 13 26 24 113 20 j half Z. for the er- 

20 39 26 116 38 2 8 o; 112 50 J rors of quadrant. 

By 



[ 2 79] 

By the firft of the above obfervations with a fup- 
pofed lat. = 47 1 5', being the refult of a former 
obfervation, and the Sun's declination (corrected for 
the longitude) == 22°3i / 51" N. and half the elapfed 
^s — i h 43 / $1'% the latitude will be founds 
47 16' 51", N. 

By the fecond obfervation, computed in the like 
manner, the latitude will be 47 16' 41", N. 

The place of obfervation on the ifland of Coudre, 
by an a&ual furvey, bears from Quebec, N. 41 ° 30', 
E. by the true meridian, diftance 5$ ftatute miles, 
= 52 marine j which gives D. latitude = 39' and 
Dep. 34 / =5o / D. longitude = 3' 20" of time be- 
tween Quebec and Coudre. 

I have here mentioned every particular relative to 
the obfervation, and as it really happened, that you 
might, with greater certainty, correct any errors that 
may be found therein. 

To prove the time afcertained by correfponding; 
equal altitudes, thofe altitudes taken within an hour 
of the tran|it might be worked feparately, remember- 
ing to fubtrad: 3' f ro ^ the fingle altitude for the er- 
ror of the quadrant. 



Remarks by the Astronomer Royal* 

HP HE inftruments made ufe of by Mr. Wrights 
-*• in the foregoing obfervations^ were a 2 feet re- 
flecting telefcope ; a pendulum clock beating half fe- 
conds y a brafs Hadley*s fextant, of about 1 5 inches 
radius, with a magnifying glafs to read off the obfer- 
vations ^ and a redtangular refervoir for holding quick- 

filver* 



[ 2 8o ] 

Silver, or any other fluid, which is (heltered from the 
wind by two glafs fides inclined to one another, and 
ground truly plane: this laft for taking the Sun's 
double altitude by refle&Ion with the Hadley's fextant. 
By a more accurate calculation of the times than 
Mr. Wright has ufed, I find the equation of corre- 
sponding altitudes, for the noon of June i to be — 5",o, 
June 2— 4 ,/ ,5, and June 3 for midnight -|~9">6* 
Hence the true time of noon, by the clock, June 1, 
was i2 h 19' io",o$ June 2, i2 h 18' 20^,0; and 
June 3, midnight, ia h iy f 1 1 ,/r , 1 5 and hence the 
true time of noon, June 3, (hould be iz h iy' 34 // >i» 
and the clock is lofing 46" per day on apparent 
time. Hence the apparent times of Mr, Wright's 
4 obfervations will come out as follows : 

App. time* 
h / // 

2 3 1 $3 No vifible impreffion made by Venus yet. 
2 52 56 Venus had made a fmall impreffion. 

2 50 19 Venus appeared completely round to the eye, and rather de- 
tached, and joined by a-ligament. 
2 50 50 The rays of light appeared at the internal contact. 

Taking Ifle Coudre to bear N. 41 30' Eaft from 
Quebec, diftant 55 ftatute miles, as, Mr. Wright 
fays, was found by an a&ual furvey 5 the diftance in 
geographical miles is 47,65. Therefore the place 
of obfervation is 35' 41" north of Quebec, and 
31' 34" eaft of it, =, 46' 32" difference of longitude, 
s=3 (/' of time* 



XXXVIII. Ex-