52 Ayrton, SypTion 'Recorder. [jVTaech, 



The great advantage of any system by whicli an automatic record is 

 obtained is, that should there be any difference between the message written 

 by the sender and the message sent out to the receiver, it is easy to find out 

 whether the mistake was made by the sending or the receiving signaller, since 

 what is printed on the slip of paper at the receiving station is entirely under 

 the control of the signaller at the sending station. 



On long submarine cables, however, such as the Atlantic, Eed Sea, &c. 

 as the battery power employed can only be exceedingly small compared with 

 that used on a corresponding length of land line, only one of the above men- 

 tioned methods of receiving messages can be adopted, viz., the motion 

 of a small magnetic needle. To render the angle large through which 

 a weak current will deflect this needle, the moment of inertia of the needle 

 has to be very small, that is to say the needle has to be short and light. To 

 see the actual motion of such a needle, would therefore be a difficult matter. 

 This difficulty, however, was overcome some years ago by Sir W. Thomson's 

 reflecting galvanometer. But the instrument is not only far too feeble 

 to produce any mark on paper, but in addition it even touched any stops 

 placed to limit its motion too feebly to act thereby as a " relay''' in complet- 

 ing the circuit of a current generated in the receiving office. 



The problem to be solved, therefore, is virtually the following : How is it 

 possible to write with a pen on paper, if only an exceedingly small power is to 

 be exerted on the pen. This Sir W. Thomson has succeeded in solving 

 in his ' Syphon Recorder.^ 



Mr. Ayrton then gave a minute description of the invention. 



The receipt of the following communreations was announced — 



1. On a new Indian Sylvia. — By W. E. Brooks, Esq., C. E., Mdwah. 



2. The Syphon 'Recorder. — By E. W. Atrton, Esq. 



3. On the Osteology of Tricenops Bersicus. — By Gr. E. Dobson, 

 Esq., M. B. 



LlBRAET. 



The following additions have been made to the Library since the meeting 

 held in February last. 



Bresentations. 

 *^* Names of Donors in Capitals. 



Notices of the Astronomical Society of London. Vols. I, II, III, and 

 XXXI. — Memoirs of the Astronomical Society, Vol. XXIX, part I. — Chinese 

 Observations of Comets, by J. Williams. — The Astrois-omical Society of 

 London. 



Eeport of the British Association, for 1870. — The British Associa- 

 tion. 



