After 60 seconds the observer is about 10 yards beyond the 26th pole. Example:–Telegraph poles are set 60 yards apart. The product is the speed in miles an hour. Second Method:–When time or space will not permit the first method to be used, allow one second for every yard of the known interval, and multiply by 2.1/22 the number of objects passed in this time. Then, if after 123 seconds the observer is half-way between the 53rd and 54th poles, the speed is 53 1/2 miles an hour. Proof:–Let x = the speed in miles per hour, y = the interval between adjacent objects. Then the number of objects passed in this time is the speed in miles an hour. Welch offered two different formulas that Holmes might have used:įirst Method:–Allow two seconds for every yard, and add another second for every 22 yards of the known interval. The calculation, as he said, was a simple one what made it simple was his knowlege, which of course Watson did not share, that the telegraph poles were sixty yards apart. Actually he noted that the train had taken approximately thirty-four seconds to cover the nine hundred yards or, in other words, it was rather more than ten per cent (i.e., 6 1/2 from sixty). If a second glance at his watch had shown him that thirty seconds had passed, he would have known at once that the train was traveling at a good sixty miles an hour. This would give him a distance of nine hundred yards, a fraction over half-a-mile.
What happened, surely, was something like this: About half a minute before he addresssed Watson, Holmes had looked at the second hand of his watch and then counted fifteen telegraph poles (he had, of course, seen the quarter-mile posts, but had not observed them, since they were not to be the basis of his calculation).
Warrack, if we may so express it, is making telegraph-poles out of fountain-pens. Roberts, in a review of the book, disagreed: Guy Warrack, in Sherlock Holmes and Music, agreed: It would have been impossible to time the passage of the telegraph poles to the necessary precision using a pocket watch. So Holmes’ scrupulous dedication to accuracy should have led him to say “between 53 and 54 miles an hour” or even “between 52 and 55.” Galbraith complained that the detective’s casual statement is “completely inconsistent with Holmes’ character.” Using the second hand of his watch, he’d had to mark the passage of two successive telegraph posts, probably a mile or more apart, and count the posts between them an error of more than one second would produce an error of almost half a mile an hour. Is it? The speed itself is plausible - trains were allowed 87 minutes to travel the route, giving an average speed of 53.25 mph, and so the top running speed would have been higher than this. “But the telegraph posts upon this line are sixty yards apart, and the calculation is a simple one.” “I have not observed the quarter-mile posts,” says Watson. “Our rate at present is fifty-three and a half miles an hour.” “We are going very well,” says Holmes, looking out the window and glancing at his watch. At the start of the 1892 story “Silver Blaze,” Sherlock Holmes and Watson set out on a train journey from Paddington to Swindon in a first-class train carriage.
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