474 



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



Nos. 12966-8. 



STOP-WATCH, DeLay, continued. 



The speed of rotating shafts can be determined by using this stop-watch in connection with a 

 special revolution counter (see No. 12968 below). Great accuracy is obtained because of the 

 fact that both the revolution counter and stop-watch are started and stopped simultaneously 

 and are in positive connection through an electric circuit. A small flash light battery gives 

 sufficient power for operating this stop-watch $20.00 



12968. STOP-WATCH and REVOLUTION COUNTER, DeLay. An accurate and reliable revolution 

 counting device. This device consists of No. 12966 Electrically Operated Stop-wateh and a 

 special revolution counter, connected together in such a manner that the time taken to make 

 any number of revolutions may be accurately determined. The starting and stopping of the 

 watch is simultaneous with the starting and stopping of the speed counter. No error can pos- 

 sibly enter in. This device is easily more accurate than any other speed counter on the market. 



The revolution counter is the best worm gear counter made and is equipped with a small special 

 attachment for this work. This attachment does not interfere with the use of the counter in 

 the ordinary manner, and it can be used for either direction of rotation. A battery of the 

 pocket flash-light type is used to operate the device. 



To use the device, the circuit is first closed, which places the watch under electrical control. 

 The stem is then pressed, which releases the hand mechanically. Placing the rubber tip of the 

 counter in the shaft center opens the watch circuit and starts the long second hand. The 

 stop-watch continues to run until the speed counter is removed from the shaft, when the elec- 

 tric circuit is again closed, stopping the second hand. Pressing the stem of the watch holds 

 the hand mechanically so that the electric circuit may be opened. After the reading of both 

 instruments has been taken, the indicators may be returned to zero and it is then ready for 

 the next reading. The revolutions may be taken for any number of seconds or the time for 

 any number of revolutions accurately determined. When great accuracy is desired a curve 

 may be plotted from which accurate readings may be taken for fractions of a second. 



Watch and Revolution Counter complete 30.00 



12969. REVOLUTION COUNTER only, of No. 12968, with battery and cords. 

 STORAGE TANKS, see Jars. 

 STOVES, see Burners. 



12974. STRAIGHT EDGE, cherry, one edge beveled; 24-inch 



For T-SQUARES, see general heading Drawing Instruments. 

 STREAK PLATES, see Arsenic Plates. 

 STROPS. Razor, see Microtome Accessories. 

 SUBERITE RINGS, see Cork Rings. 



10.00 



.35 



