336 SEC. 10. ELECTRICITY. 



wire in centre of field of coil composed of two bobbins of fine copper wire. 

 Micrometer screws to adjust zero by torsion of upper and lower parts of 

 platinum wire. The first words transmitted across the Atlantic were from the 

 " Agamemnon " approaching the Irish coast, and were read on one of these 

 instruments on board the " Niagara " approaching Newfoundland. (Encyclo 

 psedia Britannica, Art. Telegraph (Electric), VII. 6, and VIII. 4.) Made by 

 White and Barr (now James White), Glasgow. 



This instrument was sent out for use on the first Ked Sea cable (1859), but 

 did not arrive until after the failure of the cable. It returned dismantled, and 

 was never set in action again. It has been superseded by the siphon re- 

 corder. Made by White and Barr (now James White), Glasgow. 



1446a. One of the First Mirror Galvanometers, made 

 for the reading of messages through submarine cables, and used for 

 that purpose at Newfoundland in 1858. This galvanometer has an 

 arrangement for altering the intensity and direction of the directing 

 force by a double motion of the directing magnet, one varying 

 its distance from the suspended needle and mirror, the other giving 

 the magnet a motion in azimuth. This arrangement is still used 

 in the Astatic Mirror Galvanometer for testing submarine cables. 



Sir William Thomson. 



1447. Ironclad Marine Galvanometer, used on board the 

 "Great Eastern" in the Atlantic Cable Expedition of 1866, and 

 subsequently by Mr. Willoughby Smith in the Mediterranean and 

 Red Sea. Sir William Thomson. 



This instrument is the first ironclad marine galvanometer, and the first with 

 suspension by stretched silk fibre instead of platinum wire. Made by James 

 White, Glasgow. 



1447 a. Differential Galvanometer, constructed specially 

 for testing the locality and nature of faults in submarine cables. 

 It is the first instrument in which shunts were used for practical 

 electrometric purposes. A shunt is applied to one of the wires of 

 the coil so as to multiply the reading of a rheostat ten times. It 

 also was used for telegraphic reading purposes and for measuring 

 the discharge from cables. It was made in 1858, and was in 

 constant use for many years. W. H. Preece. 



1447b. Thomson's Mirror Galvanometer, with hinged 

 coils, and Shunt for same. Warden, Muirhead, and Clark. 



1447a. Sir William Thomson's Astatic Mirror Galva- 

 nometer, with hinged coils, for testing purposes. 



Warden, Muirhead, and Clark. 



1447b. Lamp for Mirror Galvanometer. 



Warden, Muirhead, and Clark. 



1447c. Portable Testing Galvanometer on gimbals, with 

 resistance coils and shunts. Warden, Muirhead, and Clark. 



