14 RATIO OF SPECIFIC HEATS. 



k — lO, /< = 2 1, 



// = .003,' (/ = .0006, 



e = 03, 

 all riuaiitities being here given in teiwns of milligiainine.s, inillinietres, and seconds. 

 T\\unf/a is veiy nearly 1 and ue obtain 



S-S, = (.^, --,),-" 



.(6) 



Hence when the gas cools dow n as far as ^^ — S^ = 150 Q^ ^ye find for 



o 



a; = o. I cm. 3 — S, = 6° C, 



.r = .5 cm. - - -1 =.i°C. 



If, therefore, the very thin .silver-free platinum film wei'e soldered directly to the stout 

 copper terminals, a fall of temperature would be manifest at the ends of the plat- 

 inum stri}), the influence of which would l)e far fi-oin negligible iu its bearing on 

 T 



In view of the intei'position of the gradually nariowing or arrow-shaped flap 

 of platinum and silver between the terminals and the effective bolometer stiip, the 

 distribution of temperature is materially changed. For the flap in (piesticm the 

 constants may be estiiuated as follows : 



k = 109, 



>> = -003. 

 c = .06, 

 A' = lo.S, 



(/ := .0066, 



all taken, as before, with reference to milligrammes, millimetres, and seconds, while 

 h is entered unfavoral)ly with a value decidedly large. In this case the iiuotieiit 

 f/a is found by computation to be .09, and the temperature distril)UtioM for 

 ^0 — ^] = 15° is now such that at a distance of 3 cm., the increment is Imt 1 V. The 

 effect of using the end flaps of silver is thus a reduction of temperature from the 

 terminals to the strip, fast enough to (piite wipe out any sei-ious discrepancy due 

 to unerpial temperature in the strips. 



In view of the good conduction of electricity by the silver flaps, fuithermore, 

 the change of resistance due to change of temperature is equally inappreciable. 

 Thus any marked discrepancy due to conduction of heat along the teiniinals to the 



' 'I'his number has been obtained for thick rods of iron and German silver. We were obliged 

 to enter it, not having found any special value for platinum. Clearly the quantity // cannot in any 

 real case be a constant. It must increase very rapidly with the decreasing diameter of a given rod. 

 Thus the value above assumed is considerably too small. For very thin rods Cardani finds // = .06 

 (Nuov. Cim., [3], vol. 30, pp. 33-60, 1891). If a larger value for // than the above is |)ut into the 

 equations, the results obtained would be more favorable to our argument than those given in the 

 text. Thus if /; = .06, and x ■= o.\ cm., £• — 9, = .14". 



