4 RATIO OK Sl'FX'IKK- HEATS. 



.UOOUO cm. Witli tlif aid nf a siiitahk- stet'l ruler ami a thin sliarjt kiiitV, we were 

 al)]e to fut a strip from tlu* foil wliidi Ix'tu'eeii the raimlly iiarrowiiiir end flaps a 

 and l> was Imt .02 t-ni. in breadth throiighniit a length <>i' about lU em. After tiie 

 end Haps (eaeh about 4 em. long and .5 em. broad) had at their extreme edges been 

 sohlered to thick copiter terminals, the middle of the strip was dipped iu concen- 

 trated nitric acid to remove the silver fi'om the jilatinum film to be used. 



'J'he resistance of the pl.-itinum bolometer strip etched otT for a length of 7 

 cm. was alxiut 8<> ohms, while the resistance of the ])arts not freed from silver was 

 computed as about .4 ohm, only .(l.'J ohm of which ni.ikes up the total resistance of 

 the flaps. 



'I'he third oi>euing of the receivei- is shown at '/; and usetl as an avenue of 

 elilii.v. Its diameter iu tiie clear was .". cm., and it was closed with a perfoi'ated 

 rubber stop|>er, through which a wide glass stopcock // was inserted. Either by 

 suildenh remo\ing the rubber stopper, oi' in like nianm^r wholly or jiai'tially open- 

 ing the stopcock II, we had il in oiii- power to vai'y the interval of exjiansion 

 within a w i<le range. 



A large zinc-lined w<x>ileii tank A', lilted with w.-itei' .and surrounding the 

 receiver served the purpo.ses of a water liath. 'Id compensate for the buoyancy 

 of the receiver, sutticient counter pressure was a})plied through the jierforated 

 wooden voke h, whi<"h on being foi'ced down by the screw a held the receiver 

 Hrmly down upon the annular tripod C. Two stiri'iug ap}tliances ^ were fitted 

 to the iliagoually opposite corners of the water bath. These consisted of zinc 

 cylinders, o])en at both ends and containing an axial jiropeller like rotating .screw. 

 Ai'tuateil ))\ ;i small electromotor these sci'ews were eflicieni in [)roilucing a flow of 

 watei' in the zinc cylindei's either from beli>w upwai'ds or in the revei'se direction at 

 pleasure. If the propelling screws within the C3dinders rotate in contrary directions, 

 a circulation of watei' in the bath will ensue fi-oni the surface downward near one 

 of the stirrers, thence along the bottom to the opposite stirrer, whicli carrying the 

 water aloft stimidates the return ciiculation along the surface. Small floating 

 bodies like .strijts of paper gave evidence of the I'ate at which the current was 

 moving. 



I). MEASITKEMENT OK TEMI'KIiA'rURK 



To i'eij;ister the leii:|ii'i;ilure of the water lialli we ii-ed .-i ca]il>rate(l thermometer 

 graduated in tenth degrees. This was read olV by a microscope of low power, 

 provided with an ocular micrometer. Continually observing this tliermometer, 

 and adding small (piantities either of cold or hot water acconling as the thermometer 

 showed a leaning toward higher or lower temperatures, we succeeded in keeping 

 the temperature of the water constant to about a humlredth of a degree. 



