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



No. F4853. 



No. F4749. 



DIAL WHEATSTONE BRIDGES. No - 



F4741. WHEATSTONE BRIDGE, Dial Decade Design. Similar in construction to Nos. F4721 Dial Re- 

 sistance Boxes listed on page 221. Has six ratio coils, one each 1, 10, 100, 100, 1,000 and 10,000 

 ohms, adjusted to an accuracy of 1/25 per cent. The rheostat has four dials, giving 10x1, 10x10, 

 10x100 and 10x1,000 ohms, a total of 11,110 ohms, and is adjusted to an accuracy of 1/10 per 



cent $131.25 



F4742. WHEATSTONE BRIDGE. Same as No. F4741, but with ten ratio coils, two each 1, 10, 100, 



1,000 and 10,000 ohms 137.50 



F4743. WHEATSTONE BRIDGE. Same as No. F4741, but with five dial rheostat, giving 10x0.1, 10x1, 



10x10, 10x100 and 10x1,000 ohms, a total of 11,111 ohms 150.00 



F4744. WHEATSTONE BRIDGE. Same as No. F4742, but with five dial rheostat, giving 10x0.1, 10x1, 



10x10, 10x100 and 10x1,000 ohms, a total of 11,111 ohms 156.25 



F4749. TESTING SET, Portable. A compact and reliable self-contained instrument, including Wheat- 

 stone bridge with rheostat, galvanometer, battery and necessary switches. The ratio arms of 

 the Wheatstone bridge are of the plug type and include four coils in each arm, 1, 10, 100 and 

 1,000 ohms. The rheostat is of the dial decade type with four dials, units, 10 's, 100 's and 

 1,000 's, giving a total resistance of 11,110 ohms. The rheostat switches may be revolved 

 continuously in either direction and the contacts are made by multiple brushes, with ends bent 

 so that they are not tangent to the circle in which they move and therefore do not wear rings 

 in the blocks. The contact blocks are on the under side of the plate on which they are 

 mounted, thus insuring a good contact, free from dirt. The galvanometer is of the suspended 

 type and has a sensibility of 1 megohm. With a galvanometer of this type, all trouble experi- 

 enced on account of the dulling of the pivots as used in old style instruments is entirely obvi- 

 ated. The resistances are the same as used in our Resistance Boxes, described on pages 220-2, 

 and are accurate to 1/10 per cent. The entire set is mounted in a finely finished hardwood 



case, with leather strap handle for carrying. Complete with directions 200.00 



F4851. RESISTANCES on Spools. These resistances are of the same quality used in our Resistance 

 Boxes and are guaranteed to be of the best workmanship. The winding is bifilar on substantial 

 wooden spools, the ends soldered to heavy copper terminals. Accurate to i/ of 1%. 



Resistance in ohms 1 2 5 10 25 50 100 200 500 1000 5000 



Each 75 .75 .75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 3.00 



F4853. RESISTANCE COILS, mounted in brass case, rubber top, with two binding posts and rubber top 

 brass taper plug for short circuiting the coil. Coils wound bifilar on wooden spools, and guar- 

 anteed to an accuracv of I/^Q of 1%. 



Resistance in ohms! 1 2 5 10 25 50 100 200 500 1000 5000 



Each 6.00 6.00 .00 6.00 6.50 7.00 7.50 8.00 8.50 9.00 10.00 



F4861. STANDARD RESISTANCES, N. B. S., as designed by Dr. E. B. Rosa of the Bureau of Standards. 

 (Bulletin B. of Stds., Vol. 5, p. 413.) In these resistances the coil is wound on a metal cylinder 

 and baked in shellac. It is supported by a small tube (closed at the bottom) which serves 

 as a thermometer tube. The leads pass through a hard rubber top which screws into the brass 

 case. The coil is adjusted to the highest precision and the case filled with moisture-free oil 

 and hermetically sealed. 



These coils have the following advantages over the old Reichsanstalt form: -(1) They are prac- 

 tically constant. Only one coil out of 28 changed as much as 2 parts in 100,000 in 12 months. 

 (2) They are more compact, the distance between terminals being only 7.5 cm. 



Resistance, ohms 1 10 100 1 .000 10.000 



Each 20.00 20.00 20.00 20.00 25.00 



