Figure 27. Im Michelson interferometeb The horizontal component oi tl 

 a< ting on the knife edge through the swinging pendulum causes the support to n 

 unison with the pendulum, and therebj affet is the period ol the osi illation. I his mi ve- 

 meni is th< so-called flexure of the pendulum support, and must be taken into account in 

 the most ai i urate observations. 



In 1907, the Michelson interferometei was adapted to this purpose b) 

 and Geodetic Survey. As shown here, the interferometer, resting on a wooden beam, i* 

 introduced into the path of a light beam reflected from a mirror on the vacuum chambei 

 Movement ol that mirror causes a corresponding movement in the interference fringes 

 in the interferometer, which can be measured. 



.is the Brown Pendulum Apparatus. 88 



The original Von Sterneck apparatus and thai ol 

 Mendenhall provided for the oscillation of one 

 pendulum at a time. Alter the adoption of the \ on 

 Sterneck pendulum in Europe, there wen- developed 

 stands on which two or four pendulums hung at the 

 same time. I his procedure provided a convenient 

 wa\ to observe more than one invariable pendulum 

 at a station for the purpose of detecting changes in 



I |. Brown, .1 Determination of I ilues of 



• • Potsdam and Washington (Special Publication No. 

 204, U.S. Coast and Geodetic Surve) . Washington, l')36). 



length. Prof. M. I laid ol Karlsruhe in 1896 d< 

 a four-pendulum appat itu Dr. Schumann ol 



Potsdam subsequently described a two-pendulum 

 apparatus. " : 



The multiple-pendulum apparatus then provided a 

 method of determining the flexure of the stand 



- M. Hun. "Neues Pendelstativ," Zeitschrift fur Imtiu- 

 mentenkuna 16, P- 193. 



1 11 R.. Schumann, "fjba eine Methode, it. is Mitschwingen 

 bei 1 <-l. 1 1 iv <-ii Schweremessungen zu bestimmen," Zeitschrift 

 fur InstTumentenhtnde (January e design 



for the stand is similar to that of Peirce's of 1 - 



I'AIM-.R 44: DI'AF.I OPMENT OF GRAVITY PENDULUMS l\ till 19TH CENTURY 



335 



