# Thread: how many telegraph posts did holmes count?

1. ## how many telegraph posts did holmes count?

extract from "Silver Blaze" - Memoirs of Sherlock Holmes

We are going well, said he, looking out of the window and glancing at his watch. Our rate at present is fifty-three and a half miles an hour.
I have not observed the quarter-mile posts, said I.
Nor have I. But the telegraph posts upon this line are sixty yards apart, and the calculation is a simple one.
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the question is "how many telegraph posts did holmes count?"

we know that 1 mile = 1760 yards

60 yards = 1 telegraph post
1760 yards = 1760/60 telegraph posts
= 29.33 telegraph posts

1760 yards per hour = 29.33 telegraph posts per hour, i.e.,
1 mile per hour = 29.33 telegraph posts per hour
53.5 miles per hour = 53.5 x 29.33 telegraph posts per hour
= 1569.155 telegraph posts per hour
= 1569.155/60 telegraph posts per minute
= 26.15 telegraph posts per minute (approximately)
= 27 telegraph posts per minute (approximately)

so, holmes must have counted about 27 telegraph posts.

2. Interesting....a little bit random....but interesting!

3. Originally Posted by Reichenbach
Interesting....a little bit random....but interesting!
what did you mean by random?

4. Originally Posted by holmesian
so, holmes must have counted about 27 telegraph posts.
That is assuming that he observed for exactly a minute.

He could as easily have counted poles for a longer period in order to derive a more accurate result, or even have extrapolated from a shorter period.

Or indeed, he could have timed the appearance of a fixed number of poles (perhaps 29.33 of them, an exact mile) and calculated from there, fixing the distance rather than the time period.

I don't believe the book states how long he was counting poles. Apart from that, I can't fault your mathematics.

5. Originally Posted by Xamonas Chegwe
That is assuming that he observed for exactly a minute.

He could as easily have counted poles for a longer period in order to derive a more accurate result, or even have extrapolated from a shorter period.

Or indeed, he could have timed the appearance of a fixed number of poles (perhaps 29.33 of them, an exact mile) and calculated from there, fixing the distance rather than the time period.

I don't believe the book states how long he was counting poles. Apart from that, I can't fault your mathematics.

yeah, i assumed that he watched for 1 minute. from the story it seems that he was looking out the window for a very short time. (We are going well, said he, looking out of the window and glancing at his watch.) that's why i assumed that he looked out for a minute.

but of course you are right too. he could have been counted poles for a longer period of time.

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