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SCIENCE. 



[Vol. XIII. No. 327 



are attached. The front of the rheostat-box is covered with glass, 

 preventing the dirt and dust from getting into the box, and at the 

 same time allowing ready inspection. 



The ampere-meter, or ammeter (Fig. 6), is an instrument to in- 

 dicate the number of amperes which the dynamo is generating 



As each lamp requires a certain current in amperes, from the in- 

 dications of the ammeter, the number of lamps burning may be 

 easily computed. This may also be left in the circuit permanently 

 without overheating. 



The lightning-arrester (Fig. 7) is simple in its operation. The 



Fig. 8 represents a main switch of the Western system for 150 

 and 300 ampdres capacity. 



Fig. 9 represents a multiple safety cut-out board. These boards 

 are convenient where a number of branches terminate in a closet, 

 and are useful to connect up a number of single cut-outs in mul- 



tiple arc. These boards are made for any number of circuits from 

 four to twelve. The safety-strips may be replaced in a few seconds, 

 and, while current is on, without danger. 



Figs. 10 and 1 1 represent ceiling cut-outs, to be used when 

 lamps are to be suspended by means of flexible cable. 



jaws of this lightning-arrester are made of carbon plates. In case 

 the dynamo-current should follow a discharge of atmospheric elec- 

 tricity, an arc may be set up ; but this will burn away some of the 

 carbon points, and thus free the dynamo of the short circuit. Such 

 a carbon lightning-arrester can, of course, only be used for low- 

 tension dynamos. 



Fig. 12 represents a double pole branch-block. 



We learn from Nature that Dr. Schweinfurth arrived at Aden 

 on March 23, on his return from a three months' stay in Central 

 South Arabia. He has started for Europe, taking a very interest- 

 ing botanical collection with him. 



