APPENDIX. 929 



1336a. Dynamo-Electric Light Apparatus. This ma- 

 chine gives a light of 4,000 normal candles with 850 revolutions 

 of the armature per minute, with an expenditure of work equal to 

 3 horse-power. Siemens and ffalske, Berlin. 



1336b. Dynamo-Electric Light Machine producing a 

 light equal to 1,000-1,300 normal candles with about 1,100 revo- 

 lutions of the induction cylinder per minute and an expenditure of 

 1 to 1^ H.P. The machine is 640 millimetres in length, 540 milli- 

 metres width, and 225 millimetres height. 



Siemens and ffalske, Berlin. 



1336c. Magneto-Electric Machine to give a constant 



current. The apparatus has 50 steel magnets, and the current 



produced is equal to that from 8-10 Bunsen's elements. The 



armature is rotated by hand. Siemens and ffalske, Berlin. 



1409. Electric Lamps, 1 small and 1 large. These lamps 

 are automatic in their motion ; in them the carbon points are caused 

 to approach or recede from each other. 



Siemens and ffalske, Berlin. 



1454. Sine-Tangent Galvanometer, for use at will either 

 as a sine or tangent galvanometer. Siemens and ffalske, Berlin. 



1455. Aperiodic Galvanometer, with telescope and scale. 



Siemens and ffalske, Berlin. 



The needle of this galvanometer is suspended in a copper ball, which acts 

 as a damper, preventing vibration in any new position given to the needle. 

 The needle itself is in the shape of a thimble cut away longitudinally on 

 opposite sides, and by this arrangement the magnetic intensity is considerably 

 increased, and the inertia of the magnet reduced. Du Bois Raymond has 

 shown that the " damping " of an astatic needle can be carried so far that the 

 needle does not vibrate, but directly takes up its position of deflection, and he 

 has termed these " aperiodically vibrating needles." Dr. Werner Siemens 

 has attained the same end with simple non-astatic magnets, by means of 

 certain forms of the vibrating magnets, and of the damping copper mass. 

 The vibrating magnet consists of a steel thimble, from which two opposite 

 sides are cut away parallel to the axis. This horseshoe magnet vibrates in a 

 cylindrical space in a copper ball, which forms the centre of the wire coils. 



1487a. Revolving Coil used in the determination of the 

 "British Association Unit of Electrical Resistance," 



1863-4. (The property of the British Association.) 



Prof. Clerk Maxwell. 



The coil forms a closed conducting circuit. As the coil revolves about a 

 vertical axis, the horizontal component of the earth's magnetic intensity 

 produces an alternating current in the coil. A very small magnet is sus- 

 pended at the centre of the coil, and is deflected from the magnetic meridian 

 by the current in the coil. When the coil revolves rapidly, the alternations 

 of the current do not produce any sensible vibration of the magnet, and the 



39508. 3 N 



