OCT. 19, 19lM parsoNvS and harper: engine r.\diators 409 



the relays operated 59 times per minute. When one ohm more re- 

 sistance was put in, causing the current to fall to 9 . 3 and 6 . 9 amperes, 

 the relays operated 38 times per minute, and the temperature within 

 the furnace fell only 0.1°. This change in the heating current cor- 

 responded to a fall of about 6 per cent in the line voltage, about as 

 large a fluctuation as is likely to occur in the voltage of a lighting 

 circuit. 



ATTACHMENT FOR STEADY HEATING OR COOLING 



If the furnace is to be used in making heating or cooling curves, 

 the adjustment of the regulator must be changed either continuously 

 or by small, frequent steps. The slide wire of the Wheatstone bridge 

 may be used for this, but it has been found more convenient to shunt 

 the 75 ohm coil of the bridge with a rheostat giving steps of 10 ohms 

 from 1000 to 2000 ohms, placed beside the potentiometer used for meas- 

 uring the furnace temperature. A 10 ohm slide wire rheostat is in- 

 cluded in the circuit and used as an alternate fine adjustment for 

 work at constant temperature. 



Figure 3 is the heating curve obtained from the melting of a small 

 sample of gold in calibrating a thermocouple. Curve I is the temper- 

 ature of the gold; II, that of a thermocouple placed a little above it; 

 and III, the resistance in parallel with the 70 ohm coil of the bridge. 

 The heating curve, II, of the furnace is not linear, but it is smooth, 

 and the cur\^e, I, furnished by the sample of gold is entirely satisfactory. 



A linear heating or cooling rate can be obtained by means of a sim- 

 ple potentiometer connected in series with the galvanometer. 



TECHNOLOGY. — Radiators for aircraft engines.'^ S. R. Parsons 

 AND D. R. Harper, 3d, Bureau of Standards. 



The technologic paper from which this article is condensed will 

 describe the laboratory investigations relating to aircraft engine ra- 

 diators which were conducted by the Bureau of Standards during the 

 World War and in the two years immediately succeeding it. Indi- 

 vidual reports covering many phases of the subject have been pub- 

 lished previously in the technical series of the National Advisory Com- 

 mittee for Aeronautics and in scientific and engineering journals. 

 These reports, however, lack the systematic coordination, uniform 

 terminology, and unified mathematical treatment which should 



' Condensed from a forthcoming official publication of the Bureau of Standards, U. S. 

 Department of Commerce. Comnmnicated by the authors with the permission of the Di- 

 rector of the Bureau of Standards. Received September .24, 1921. 



