Box Tunnel - Brunel's Birthday

Brunel's Birthday

There is a story which states that Brunel deliberately aligned the tunnel such that the rising sun is visible through it on 9 April each year, his birthday. Opinions vary widely as to whether this is true. Angus Buchanan (2002, p. 269) writes:

The alignment of the Box Tunnel has been the subject of serious discussion in the New Civil Engineer and elsewhere. I am grateful to my friend James Richard for making calculations which convinced me that the alignment on 9 April would permit the sun to be visible through the tunnel soon after dawn on a fine day.

On the other hand, it has been asserted that it is impossible to guarantee the effect on a particular calendar day, because the angle at which the sun rises on a given date varies slightly with the cycle of leap years. However, the sun subtends an angle of about half a degree, which is more than the year to year variation, and more than the field of view through the tunnel, so it quite possibly seems to fill the tunnel every year. It is also asserted that Brunel failed to account for atmospheric refraction and the effect is visible a few days too early.

Buchanan (p. 226) concludes:

...I have found no documentary evidence for the often-repeated story that Brunel aligned the Box Tunnel so that the rising sun shone through it on his birthday, even though careful examination shows that it could indeed do so, and it is certainly a good story.

It is tempting to think that with a suitable vantage point, the effect (if not Brunel's intentions) can easily be checked on 9 April. However, the appropriate point is in the middle of a high-speed railway line and is thus potentially very dangerous. Photographs of the effect have reportedly been taken with appropriate assistance from railway officials.

A similar situation exists with the Voortrekker Monument in Pretoria, South Africa. At midday on the Day of the Vow, the sun (if the weather is clear) shines straight down onto a stone with the Afrikaans inscription, "Ons vir jou, Suid-Afrika" ("Us for you, South Africa").