Lags of Thermometers. 69 



This thermometer was mounted by itself on the top of a 

 wooden block, the centre being 5 cm. above the top and 

 near the edge of the block. An aluminium pointer 19 cm. 

 long was fitted, and a scale, marked off in degrees, was 

 mounted on the side of the block under the pointer. The 

 scale could easily be read to '1 division (*3° C). The 

 thermometer was heated in the dry inner vessel of a copper 

 calorimeter, heated water being in the outer vessel and the 

 block resting on the rim. When the temperature of 

 the spiral was about 81° C. (room temperature 17° C.) the 

 block was quickly removed, and the thermometer placed on the 

 -axis of a 30 cm. fan at a distance of 120 cm. from it. The 

 air velocity at this distance, measured by manometer, was 

 from 5 to 10 m.p.h. Times measured from the instant of 

 removal and positions of the pointer were simultaneously 

 recorded. In the first orientation the spiral cylinder was 

 broadside to the fan draught. In the second it was end-on. 

 In the latter position, about half the opening at each end 

 was blocked by standards supporting the axis of the spiral 

 cylinder, but there was a clearance between these and the 

 spiral of at least 0*6 cm. The following table gives the data 

 obtained, t being the time, ljp x the fractional drop in the 

 ** broadside " position, and l/p 2 the same in the " end-on " 

 position. The values of r pi an( i P2 are means from two 

 experiments in each position. Experiments in the same 

 position showed good agreement. 



t- 



Pv 



P 2 - ] 



°g*.Pi/loge# 



o 3 



1-00 



TOO 



— 



15 



1-73 



1-54 



1-27 



30 



292 



2-38 



1-24 



45 



5-29 



3-58 



1-31 



60 



8-46 



5-18 



1-30 



90 



20-9 



10-02 



1-32 



120 



49-1 



16-2 



1-40 



150 



80 



232 



1-39 



180 



113 



35-4 



1-32 



210 



200 



55 



1-32 



240 



310 



75-2 



1-33 



270 



620 



93 



1-42 







Mean 



.... 1-34 



Hence hi/h 2 = 1*34, that is, turning the thermometer from 



