>A few years ago, I read an article about the famous Box
>tunnel, where Isambard Kingdom Brunel was reputed to have
>completed the design so that the sun shone directly through
>it at dawn on his birthday, 9th April. The article cast
>some doubt on the truth of this assertion.
>I thought that the article was in a British Sundial Society
>Bulletin, but I can't find it.
>Can anyone point me towards it?
>
>Mike Shaw
I am not aware of the BSS article and would also be interested. There
is an analysis in the New Civil Engineer, 4th April 1985 pp29-31. That
article and my own analysis below suggest that the sun does not
shine through the tunnel on 9th April, Brunel's birthday, but does do
so on 7th April.
The light through the tunnel on his birthday would be very bright and
could be mistaken for direct sunlight - especially on a photograph.
Brunel certainly had the means and ability to make the necessary
slight changes in alignment to thus illuminate his birthday morn.
It appears that he did not do so.
The tunnel azimuth is some 79d 35' and the track has a gradient of 1 in 100
rising to the east (altitude 34'). The far opening subtends a vertical
angle of 13' from the other end - the corresponding horizontal angle is 11'.
The tunnel was designed in the early 1830s. Data for 1835 are:
Date time (UT) solar azimuth solar altitude
(corrected for
refraction)
April 7**** 05.40 79 38 (tunnel 79d 35') 0 37' (tunnel
34') ***
April 8 05.38 79 05' 0 39'
April 9 05.35 78 19' 0 35'
Taking into account the sun's angular diameter and the opening size,
sunlight passed directly through the tunnel on 7th April. It does not do
so on Brunel's birthday, 9th April - when the sun as at the 'correct'
altitude its azimuth is incorrect.
Les Cowley
[EMAIL PROTECTED]
