236 Intelligence and Miscellaneous Articles. 



I wished to ascertain whether the presence of iron exerted any 

 influence upon the results, and therefore enclosed the mercury of 

 one of my copper cylinders in a cylinder of iron which weighed 

 900 grms. For the difference of both oscillations we now obtained 



0"'000702 ; 



hence the influence of the iron may be regarded as almost null. 



From the whole number of my observations, I conclude that with 

 a pendulum 10 metres long, when it rotates conically from west to 

 east, the angular velocity at Paris is retarded 11 "*4 per second of 

 time ; on the other hand, when the motion is from east to west, the 

 velocity is increased by the same amount. 



From these observations the length of the simple seconds pendu- 

 lum may be deduced when the following corrections are taken into 

 account : — 



1. The effect of temperature. 



2. The loss of weight by the air ; according to Dubuat, Bessel 

 and Poisson, the motion of this fluid must also be taken into account. 



3. The sinking of the centre of oscillation under the centre of 

 gravity. 



4. The diurnal course of the chronometer or of the clock. 



5. The effect produced by the weight of the suspension-wire on 

 raising the centre of oscillation, an effect which in my experiments 

 amounted to 10*6 millims. 



6. Finally, the bending of the wire to the form of a catenary by 

 the simultaneous action of its weight and its centrifugal force. From 

 this it follows that the lowest tangent to the wire, prolonged to the 

 axis of rotation, would intersect the latter at a point which must be 

 regarded as the true centre of the upper suspension of the wire. I 

 find by calculation that a subtractive correction is thus rendered 

 necessary, which is almost the same as the foregoing, and in my 

 experiments rises to 10*5 millims. 



Applying these corrections, I find the length of the simple seconds 

 pendulum at Paris =993*77 millims., which differs but little from 

 993*86 millims., the length assumed. 



It is important to remark, that the correction, on account of the 

 bending of the wire, as far as I know, has never been applied to the 

 plane oscillations of a pendulum suspended by a wire ; that made 

 use of by Borda in 1792, for example, had no such correction ap- 

 plied to it. This correction, however, seems just as necessary in 

 the case of the plane swinging pendulum as in that of the conical 

 one. As the value of this correction may be very perceptible, the 

 subject is well worthy the attention of the calculator and of the ex- 

 perimental physicist. — Comptes Rendus, vol. xxxiii. p. 195. 



EXAMINATION OP A RED VARIETY OF MOLYBDATE OP LEAD PROM 

 PHOINIXVILLE, U.S. BY CHARLES M. WETHERILL, PH.D. 



In the Proceedings for the 30th March of this year is a descrip- 

 tion of a red variety of molybdate of lead, examined qualitatively 



