20 



VALUE Or THE FACTOE IN UTGBOMETRIC EOEMl'L-E. 



near 32° : — 1st. If the air is a little above, and has been below 32°, 

 there will frequently be a small button of ice at the foot of the wet 

 bulb thermometer which is not easily perceived, and which will keep it 

 at 32° when the temperature of evaporation is really above that point. 

 2nd. It is well known that under certain circumstances water may 

 be cooled below 32° without freezing, and an example will perhaps 

 • the error which this may occasion. Let us suppose that the 

 temperature of the air is 27 c ', and that when the thermometer is 

 wetted it sinks to 26° aud then rises. Should it rise very slowly the 

 probability is that 26° is the true temperature of evaporation, but if 

 rapidly, the rise may be due to the conversion of the water into ice, 

 and it will be prudent to observe whether or not the thermometer 

 again commences to sink. We have frequently observed this phe- 

 nomenon, and I am quite at a loss to what to ascribe its uncertainty. 

 It-has occurred both in a high wind and a calm, (the thermomel 

 are protected from the full force of the wind.) and it also appeared 

 to be quite uncertain at what temperature the water would fr< 



iged to admit that the limits of certainty of the factors 

 below zero are not so close as could be desired. This is partly 

 attributable to our having to reject many observations made Avith a 

 thermometer which was broken before its index errors were fully 

 ascertained. Mr. Campbell and I must claim the indulgence of those 

 who know the difficulty of taking observations requiring so much 

 time and accuracy, at such temperatures, and frequently at six o'clock 

 in the morning;. 









Probable 



datum. 



error 



factor 



Mca rure 

 of 



It is, therefore, 



Temperature 



Factor. 



- 



- 

 datum. 



an equal chance 

 factor 



{') 



(/) 



(,,.) 





(/<) 







ween. 



48° — 51" 







.30 





.07 





2.24 I 



ft 





13 



. 





.07 







42 - 





41 



. 



1.189 



.06 





2.J7 







17 



.41 



1.163 



.10 





2.73 

















— 2.92 





3.02 



64 





1.114 



.05 





. 







20 





















.775 









- 





27 





.723 







4.27 — 





5.46 



43 





.:.; 7 



.!•; 







22 - 



■ 



16 



1.20 





.81 











6 







."7 





— 7.50 



IS — 19 



7 13 



21 





.::::i 



31 



i 517 



: — 7. 1 1 



17 







1.76 



.271 





1.209 



7 21 — 7.99 



14 — 15 





17 



1.7-2 



.277 



.12 



1.141 



5 — 939 





10.30 



20 









.842 



1036 



ID — 11 



11. 50 



11 



2.19 





.66 



.723 





8—0 



13.06 









1 .6 I 



.292 



11.42 - i 



: 



15.30 



7 





.180 









(i — .-, 



16.28 



11 



1.-7 



.255 





.055 



15.73 — ID 73 



-1 — -4 



19.37 



10 





.116 



130 



367 



18.07 — 2D.D7 



- -10 



81.64 



6 





.102 



L90 



.251 



19.74 — - 



-11 - 















.107 



5 - 12.31 



