272 SEC. 10. ELECTRICITY. 



1341. Delezenne's Circle. An instrument for developing 

 electrical currents by the agency of terrestrial magnetism. 



Elliott Brothers. 



1342. Apparatus by which Forbes procured an Induction 

 Spark from a Natural Magnet. Trans. R. S. Edin., 1833. 



University of Edinburgh. 



II. APPARATUS FOR REGULATING THE PLACE 

 AND TIME AT WHICH THE EFFECTS OF AN 

 ELECTRIC DISCHARGE OR CONTINUOUS ELEC- 

 TRIC CURRENT ARE PRODUCED. 



1343. Six Specimens of Tubular Binding Screws for 



making electrical connexions. George Gore, F.R.S. 



1343a. Specimens of Wire for Electric Apparatus. 



1. Copper wires, covered with gutta-percha (1, 2, 25). 



2. Copper wires, covered with gutta-percha and cotton (3). 



3. Copper wires, covered with cotton (4, 5, 6, 9, 11, 12, 13, 14, 

 26). 



4. Copper wires, covered with silk (7, 8, 10, 15 to 23, 27). 



5. Elastic poires, with their cordons (24). 



6. Wires covered with various metals, with statement of their 

 resisting power. Madame Bonis, Paris. 



1344. Double Terminal, by Captain R. G. Scott, R.E., to 

 show the direction in which the spark tends to travel. 



School of Military Engineering, Chatham. 



1345. Single Plug Key, to close or break contact for long or 

 short durations. Elliott Brothers. 



1346. Pall-hammer, to obtain perfect equable closing of a 

 circuit. 



Prof. Engelmann, Physiological Laboratory and Ophthal- 

 mological School, Utrecht. 



On a brass prismatic lever, movable round a horizontal axis, slides the 

 bridge, a copper cover having underneath two amalgamated copper points. 

 On depressing a spring the lever falls from a nearly vertical position, and 

 plunges the bridge into two mercury vessels, movable on a horizontal sledge, 

 and connected with the battery. A spring prevents the bridge from rebound- 

 ing. Velocity of fall to be regulated by moving the bridge on the lever with 

 corresponding displacement of the mercury vessels on the horizontal sledge. 



T>y using the bridge as branch-closing, equable breaking (more correct 

 diminishing) of a current may be obtained. The bridge being in the primary 

 circuit of an induction apparatus, the breaking is every time to be effected at 

 another place of the circuit, before lifting the bridge from the mercury, iu 

 order to prevent oxidation of the mercury by the spark. 



The instrument can easily be managed with one hand. 



