104 A. L. Day and B. B. Sosman — 



tribution of temperature over the surface of the bulb was 

 therefore undertaken. 



Since the number of wires which could be led out through 

 the packed joints was limited, the plan was adopted of using 

 the bulb itself as a differential thermoelement, single platinum 

 wires being tied to the bulb at points whose temperature was 

 to be determined. Each of these wires formed, with the 

 platinum of the standard element tied to the bulb at the mid- 

 dle, a differential element which would read zero if the wires 

 were alike and if no difference of temperature existed between 

 the two points on the bulb. 



The relation of the wires was established by sealing each in 

 turn to the platinum of the standard, and measuring their 

 E.M.F. at various temperatures. The readings varied, accord- 

 ing to the quality of the wire, from to 40 microvolts. The 

 method of evaluating differences of temperature, when such 

 existed, is discussed on page 118. 



The distribution of temperature lengthwise of the bulb was 

 first investigated, and auxiliary wires were placed at the levels 

 1 (base of stem), 2 (top shoulder), 6 (bottom shoulder), 7 

 (bottom, outside of funnel), in addition to thermoelements at 

 4 (middle outside), 8 (inside reentrant), and 9 (bottom, just 

 inside of funnel).* 



With this system of thermoelements, it was found that at 

 1082°, when 9 was brought to equality with 4 and 1, the bot- 

 tom of the bulb was superheated 6 to 8° at position 6, and 

 about 4° at 7, due entirely to the fact that the thermoelement 

 at 9, not being in contact with the bulb, lost sufficient heat by 

 conduction and radiation downward to keep its temperature 

 below that of the metal surrounding it. The element at 8, on 

 the other hand, received heat by conduction up the reentrant 

 tube and by radiation from below, which made it read higher 

 than the element at the same level outside. The element at 

 position 9 was therefore discarded and each setting of tem- 

 perature made with reference only to the elements which were 

 attached directly to the bulb. 



The temperature between the middle and the top shoulder 

 was also examined in several experiments. The temperature 

 at this position was found to be within 0*5° of the other two, 

 with a tendency to be lower than these. 



Further experiments showed that in addition to the possi- 

 bility of vertical variation of temperature, there was a varia- 



* The system of numbering the positions of elements on the bulb is shown 

 in fig. 1. The figure before the decimal point indicates the horizontal level, 

 the figure after the decimal indicates the orientation around the bulb. For 

 instance, an element in position 3*5 would be about half way between the 

 top and middle and on the side of the bulb away from the front of the 

 apparatus. 



