E. Merritt — Peculiarities in Behavior of Galvanometer. 417 





I. 



II. 



Mean. 



P 2 3 



38-52 



38-76 



38 64 



FeO 



25-29 



24-82 



25-05 



MnO 



15-45 



15-64 



15-54 



CaO 



5-42 



5-64 



5-53 



MgO 



1-56 



1-44 



1-50 



Na 2 



7-46 



(7 46) 



7-46 



K 2 



200 



(2-00) 



2-00 



Li 2 



(•28) 



•28 



•28 



F 



•69 



(0 69) 



•69 



Ignition 



■73 



(0-73) 



•73 



Gangue 



2*49 



2 44 



2-47 



(R a ) 12-02 

 " 2-12 



At. Eq. 



54-16 54-66 



34-78 



17-40 



9-87 



400 y 81-20 1-5 



oxygen 



1-00 J 

 223- 223-00 4-09 



99-89 99-88 9989 



This ratio 1 : 1/5": 4-09 or 2:3:8 indicates P 3 P 2 8 as the 



i ii 



formula for the mineral in which the ratio of R 2 : R is 1 : 4*4 or 



i ii 



2 : 9 giving as molecular formula 2(R 2 ) 3 P 2 8 -[-9P 3 P 2 8 or better 



4R 3 P0 4 + 9R 3 P 2 8 . The ratio of R 3 P0 4 to R s P 2 8 in triphyl- 

 ite is 1 : 1 but here it is 1:2^, too wide a deviation to admit of 

 their being regarded as identical. 



Art. LI. — Note on Certain Peculiarities in the Behavior 

 of a Galvanometer when used with the Thermopile • by 

 Ernest Merritt, M.E. 



(Contributions from the Physical Laboratory of Cornell University, No. 8.) 



When a galvanometer, whose needle is not too thoroughly 

 damped, is used in connection with a thermopile, a curious 

 phenomenon is observed. On suddenly exposing one face of 

 the pile to some source of radiant heat, the needle of the gal- 

 vanometer moves quickly to one side. In a short time^ 

 however, the motion becomes less rapid, and in the course of 

 a few seconds the needle comes to rest, and in many cases 

 moves backward for a short distance. This behavior is then 

 repeated, and it is only after a long series of such throws, 

 which gradually become less and less marked, that the final 

 steady deflection is reached. The curve OAB in iig. 1 rep- 

 resents graphically this peculiar motion as observed in the case 

 of a Thomson tripod galvanometer, the abscissa of any point 

 on the curve showing the time that has elapsed since the 

 beginning of the motion, and the corresponding ordinate 

 being proportional to the deflection of the needle from its 

 position of rest. With a galvanometer whose needle is more 

 nearly u dead beat " the maxima and minima which are so 

 clearly shown in the figure, may not be present ; but the 

 general form of the curve will still be the same. 



