A. Einstein writes the following on The Principle of Relativity, p. 41:(adsbygoogle = window.adsbygoogle || []).push({});

"Let there be given a stationary rigid rod;and let its length be L as measured by a measuring-rod which is also stationary. We now imagine the axis of the rod lying along the axis of x of the stationary system of co-ordinates, and that a uniform motion of paralell translation with velocity v along the axis of x in the direction of increasing x is then imparted to the rod. We now inquire as to the length of the moving rod, and imagine its length to be ascertain by the following two operations:-"

my concern is the following operation (b):

"(b) by means of stationary clocks set up in the stationary system and synchronizing in accordance with chapter 1, the observer ascertains at what points of the stationary system the two ends of the rod to be measured are located at a definite time. The distance between these two points, measured by the measuring-rod already employed, which in this case is at rest, is also a length which may be designated 'the length of the rod.'"

the present period of time is from 2:00 am thru 3:00 am, 9/5/2006, in burbank, california.

let the observer ascertain that the points of the stationary system (corresponding to the two ends of the rod to be measured) are located at 2:00 am and then at 3:00 am.

the present period of time then is the definite time at which the observer ascertains at what points of the stationary system the two ends of the rod to be measured are located.

shouldn't the "length of the rod" be implied in (2:00 am thru 3:00 am) = ("length of the rod") / v? if not, why? thanks! (2:00 am thru 3:00 am, 9/5/2006)

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# Concerned on the relativity of lengths

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