632 KANSAS CITY REVIEW OF SCIENCE. 



From January 20th to February 20th, the period embraced in this report^ 

 there has been steady cold weather with but little snow. 



On the loth of February the temperature was -16.75°, ^'^d ^^ ^^ ^6th it 

 was -17.5°. These were the lowest temperatures recorded this year to the pre- 

 sent date. The loth was the coldest day, the usual mean of the three regular 

 observations being -7.08°. 



A comparison of temperature observations of the last few years for January 

 and February may be of interest : 



If February continues cold for the next seven days these two months in the 

 present winter will be the coldest of the past five years. The extreme low tem- 

 peratures of 1883 and 1884 have not been reached, but the below zero days have 

 been more numerous, and the mean temperature lower. 



THERMOMETERS. 



The severity of the past winter has invested thermometers with an unwonted 

 interest, and it may not be unprofitable, at least to younger readers, to devote a 

 short time to a discussion of the various kinds in most ordinary use. 



As the expansion and contraction of the substance in the thermometer-tube 

 indicates the amount of heat or col.d prevailing, the definition of heat as a very 

 rapid reciprocal motion of the small particles or molecules of matter is very ap- 

 propriate, for heat expands all bodies, probably by producing more commotion 

 among and causing their molecules to occupy a larger space. Liquids expand 

 more than solids in proportion to the heat applied, and hence are ordinarily used 

 rather than solids for thermometrical purposes ; though some of the latter are proba- 

 bly more accurate and delicate, but less adapted to the more common uses of the 

 instrument. Thermometers are based upon the facts that heat expands sub- 

 stances and that the same substance always possesses the same volume at a given 

 temperature. Hence the liquid within the thermometer-tube should increase in 

 volume to a much greater extent than the substance of the tube itself; otherwise 

 it would not rise, but merely fill the expanded tube as before the heat was applied. 

 Mercury and alcohol are the liquids used in the thermometers of the present day. 

 In earlier times the air-thermometer was used, but of course was very unreliable 

 as a heat measurer. 



The thermometer was invented in the 1 7th century, and is attributed variously 



