492 Geological Society. 



of cotton-covered iron bonnet-wire wound in the form of an 

 anchor-ring having a mean diameter of 6 cms. and thickness 

 i cm. Bound this is wound the secondary coil of about 160 

 turns of no. 22 silk-covered copper wire, forming a single layer 

 completely round, and outside this the primary of about 190 

 turns of similar wire. A condenser C of 4 microfarads ca- 

 pacity was connected across the mercury-break K to diminish 

 the sparking. One small accumulator B sufficed to work 

 the fork vigorously, the mean current consumed being about 

 2 amperes. By increasing the number of turns of wire, much 

 less current would be required, but there would be a limit, 

 since the lag must not be so great as to interfere with the 

 proper timing of the impulses. 



An alternative method, using far less current but requiring 

 two contacts, is shown in fig. 2. 



Fig. 2. _ 



MiilillllllllillllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllNII TT.iV. 



, — =• — aT 



Ml ^ 



%lllllllllllllllllllllllllilll)llllllllllllllllllllllllllllllllllllllllllllllHIIIIIISI j£ X 



The contact K t charges the condenser and K 2 discharges 

 it. The currents of charge and discharge are both taken 

 through the electromagnet M, and the action is the same as 

 above, the fork being, of course, polarized. It would be 

 necessary to wind the magnet M with many turns of wire, 

 to use a battery of high E.M.F. and a large condenser. The 

 latter, however, could probably be replaced by a polarizable 

 battery of platinum or lead wires in dilute sulphuric acid. 

 Except for economy of working, it is not so good a method as 

 the first, as the adjustments of the contacts J^ 1 and K 2 must be 

 very exact. 



As regards magnetizing the fork, there can be no real objec- 

 tion to that, for in the usual method of driving it soon acquires 

 a polarity. In fact the fork I first tried worked at once 

 without any further magnetization. 



LIX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 144.] 



November 6, 1889.— W. T. Blanford, LED., F.R.S., President, 



in the Chair. 



HPIIE following communications were read : — 



-*- 1. " Contributions to our Knowledge of the Dinosaurs of the 



"Wealden and the Sauropterygians of the Purbeck and Oxford Clay." 



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



