- ' 5KAJ SES : KLAUS 7 



"-- - '- "' - _ citv 



: the nul - a en by 



0, _ 



stant 



d6 

 It 



Tt = ~~ ' ' - ' " 



- the ri - -..mum wh 9 = . I -. i - 



and a m i nimum when - = -. - - etc. Let this nut be ent into two 



sndicoJai I ite - and let one of the two 



". .n the angle -. say. If now the two'nuts 



- - - ■--- with refe each other and th screw be 



ro* 81 - :t angular 9 bef . : he maximum velocity 



of one nut will take place at the same time that the other nut hag - 



minimum ? j, and hence the motion of one nut with reference to 



ill be a to-and-fro motion . by J) = _ - - 



D is the die the 1 - This is lependent 



- 



and hence the screw may be turned by hand and with any angular 



:ity. and as D - _ply the >: nee from one nut to the other, 

 which is unaffected by any longitudinal displacement of the it is 



evident that we are entirely independent of errors in end bearings or 



to do, tl re, is to m-r - D, r rather 



the variation in D, as the aca - h can be donebvmount- 



tate of a Fabry and Perot interferometer on one nut and the 



r on the second nut. and observ the motion of the fringes when 

 the screw is rotated. The method is very sensitive. The maximum 



: of one plate of the interferometer with reference to the other is 1 

 and if we messm : & of a fringe of srreen mercurv h^ht the smallest 



^oreable value of D wiU be of an inch. C, = # « # j d> » 



of an men. and Uns ight to be easily measurable. A much sm. 



-rd. 



The author also d :- • - Rowlands' method of ' : —ruling." The 

 thod cor- - - in ruling a large number of lines and then" turning 

 _ a a small angle) the plate^upon which the rulimr was done, and 

 again ruling the same number of lines so as to be able to • - the 

 loci of the int-r. s of the tw - - ,... If the error is a simple 



- .die on nofinten - ill simply be a sine curve. The 



"- - . graph showing . ---: "ulingfi with different adjust- 



ments of the parts of th 15, I machine. 



jticro-chemica: Teste for Identification of Varieties of Glass.* 

 - md R Grroschni? give the following scheme for identification 

 :' . see by chemical tests : — 



1. Roughly scratch with a file an area on the glass of a few square 



* I ----- _ 1910) pp. il-5. 



