346 SEC. 10. ELECTRICITY. 



1506a. Normal Mercury Unit in glass spiral. 



Siemens and Halskc, Berlin. 



15O4g. Clark's Standard Element. 



Warden, Muirhead, and Clark. 



This is the most constant voltaic cell known as regards electro-motive force. 

 It is used as a practical standard of electro-motive force. The poles are pure 

 zinc and mercury. The exciting paste is composed of protosulphate of 

 mercury boiled in a saturated solution of sulphate of zinc. 



XI. APPARATUS FOR THE APPLICATION OF 

 ELECTRICAL PRINCIPLES TO PRACTICAL PURPOSES. 



a. TELEGRAPHIC APPARATUS. 



1652. Electric Telegraph, original apparatus as it was made 

 under the direction of its original discoverer, Th. Sommering, in 

 Miinchen, 1809. K. Sommering, Frankfort. 



1653. The Volta's File, then used for the above, together 

 with the 10 original silver, and 10 original zinc plates. 



K. Sommering, Frankfort. 



1654. The Original Conducting t Wire, as it was made 

 under the direction of the discoverer in 1809-1811, and tested in 

 the Isar. K. Sommering, Frankfort. 



1655. Alarum belonging to Sommering' s Telegraph. 



K. Sommering, Frankfort. 



1508c. Portion of the original Telegraph, laid by Sir 

 Francis Ronalds in 1816, in his garden at Hammersmith, and 

 described in his book in 1823. Latimer Clark, Westminster. 



The original wooden model of the dial of the instrument used with the 

 above telegraph. 



ISOSaa. Electric Telegraph. A portion of the original 

 copper wire and glass tube buried by Sir Francis Ronalds in 1816 

 for the purpose 6f his then new discovery of electric telegraphy ; 

 found after several months' search by the exhibitor in 1862. 



Captain Henry Hill. 



loOSaa. Two Drawings illustrating plans by Sir Charles 

 Wheatstone, in 1840, for the manufacture of submarine electric 

 telegraph cables, and proposed plans for laying the same. 



Sir Charles Wheatstone. 



