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CENTBAL SCIENTIFIC CO., CHICAGO, U. S. A. 



No. F4701. 



No. F4703. 



RESISTANCE BOXES AND WHEATSTONE BRIDGES 



In the construction of our resistance boxes we use high grade rubber plates for the tops, of sufficient 

 thickness to insure a firm anchorage for the brass bars, and the best obtainable wire. 



All coils are wound bifilar in uniform layers and are practically free from inductance and capacity 

 so that any of the boxes may be used in conductivity experiments with alternating currents. The coils 

 are securely fastened to the top, so that there is no danger of the spools breaking loose and destroying 

 the connections. 



Our plugs are provided with knurled hard rubber tops moulded on, which prevents removal. The 

 plugs are carefully fitted, giving good contacts, and are placed sufficiently far apart to insure easy 

 manipulation. The brass blocks are heavy and separated so that the insulation between may be cleaned. 



We guarantee, without reservation, all our boxes to be accurate within the per cent, claimed, and 

 any boxes will be replaced that show faulty construction or do not come up to the guaranteed accuracy 

 when compared with reliable standards. 



F4701. RESISTANCE BOX, Spring Contact Design. The greatest objection to the plug form resistance 

 box, when used by inexperienced workers, is the unreliability of the contacts, caused either by 

 the loosening of the adjoining plugs when one is withdrawn or by a loose fit, caused either by 

 exchange or failure to properly insert the plugs. As will be noticed in the above illustration, 

 these dangers have been obviated by the use of the spring contact, which, on account of the 

 taper, fits tightly all points of the plug, causing no irregular wear. The external resistance of 

 the box has not been materially increased. The total resistance is 111 ohms, divided as follows: 

 0.1, 0.2, 0.3, 0.4, 1, 2, 3, 4, 10, 20, 30 and 40 ohms. The coils are guaranteed accurate to 1%. 

 10.00 



F4703. RESISTANCE BOX, Standard Design, for individual student use. We believe this box will be 

 found to be superior to any sold at an equal price. The total resistance is 111 ohms, divided 

 as follows: 0.1, 0.2, 0.3, 0.4, 1, 2, 3, 4, 10, 20, 30 and 40 ohms. The coils are guaranteed accu- 

 rate to % of 1%. For detailed description of construction, see above 12.00 



F4704. RESISTANCE BOX, same as No. F4703, but with guaranteed accuracy, %% 15.00 



F4705. RESISTANCE BOX, same as No. F4703, but with total resistance of 1,111 ohms, divided as fol- 

 lows: 1, 2, 3, 4, 10, 20, 30, 40, 100, 200, 300, 400 ohms. Guaranteed accuracy, %% 17.50 



F4711. RESISTANCE BOX, Standard Design, with traveling plugs. The blocks are of new and im- 

 proved form, which enables the coils to be held more firmly in position, and lessens the danger 

 of imperfect contact between coils and blocks. The traveling plugs add greatly to the useful- 

 ness of the instrument, making it available for the comparison of the E. M. F. of batteries 

 and other tests by the potentiometer method. The total resistance is 1,111 ohms, as follows: 

 0.1, 0.2, 0.3, 0.4, 1, 2, 3, 4, 10, 20, 30, 40, 100, 200, 300 and 400. For detailed description of con- 

 struction see above. Guaranteed accuracy, %% 45.00 



