72 Intelligence and Miscellaneous Articles. 



that the divisional planes, with which the foliation appears to be 

 parallel, may be planes of original stratification, yet, as a matter of 

 fact, they are nothing more than structural planes of some sort, 

 between which the rocks exhibit divers lithological characters. 



3. " On Fossil Chilostomatous Bryozoa from New Zealand." By 

 Arthur Wm, Waters, Esq., F.G.S. 



December 15. — Prof. J. W. Judd, F.R.S., President, in the Chair. 

 The following communications were read : — 



1. " Notes on Nummulites elegans, Sow., and other English Num- 

 mulites." By Prof. T. Bupert Jones, F.R.S., F.G.S. 



2. " On the Dentition and Affinities of the Selachian genus 

 Ptychoclus, Agassiz." By A. Smith Woodward, Esq., F.G.S. 



3. " On a Molar of a Pliocene type of Equus from Nubia." By 

 E. Lydekker, Esq., B.A., F.G.S. 



X. Intelligence and Miscellaneous Articles. 



ON A NEARLY PERFECT SIMPLE PENDULUM. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 TN an article by Mr. Thomas Gray, communicated a few days ago 

 ■*■ to the Philosophical Magazine *, he has described experiments, 

 carried out in conjunction with myself, on the oscillations, in a 

 Sprengel vacuum, of a torsion vibrator hung by a single silk fibre. 

 The performance of the tiny vibrator were so remarkable, that we 

 are proposing to carry the experiments farther ; but in the mean- 

 time they have led me in a somewhat different direction. With 

 the assistance of Mr. Gray, I have suspended a small shot a little 

 more than j 1 ^ inch in diameter by a single silk fibre (half a cocoon- 

 fibre) two feet long. This I have placed in a glass tube about three 

 quarters of an inch in internal diameter, and have exhausted with 

 the Sprengel pump to about 0*1 |V| (one tenth of a millionth of an 

 atmosphere). A most perfect " simple pendulum " is thus obtained ; 

 and I find that starting it with a vibrational range of | inch on 

 each side of the middle position, the vibrations are very easily 

 countable at the end of 14 hours. 



The weight of the lead shot used is only ^ gramme ; and a single 

 silk fibre will bear nearly three grammes. I am proceeding to make 

 a " seconds " pendulum, 39-1 inches long, with a heavier weight 

 than that used at present, and it will be enclosed in a much better 

 vacuum than 0*1 |Y|. With such a pendulum, I hope that I may 

 obtain a still slower subsidence ; and I propose to find, if possible, 

 whether the subsidence observed is due to residual air, or to 

 viscosity of the fibre. Tour obedient servant, 



The University, Glasgow, J. T. Bottomlet. 



December 14, 1886. 



* See p. 46. 



