HOW TO STUDY METEOROLOGY. 
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period to have been 51*6°, and the range 21*8°, both of which 
should be entered in columns of the observer’s book provided 
for the purpose. 
Many forms of self-registering thermometers have been con- 
trived, but I deem it unnecessary to speak of more than three 
here; viz., Sixe’s, Eutherford’s spirit minimum, and Phillip’s 
mercurial maximum. Sixe’s provides for the registration of 
maximum and minimum temperatures by a single arrangement. 
It is a handy instrument, and a well-made specimen will give 
good results to within whole degrees, but it is liable to get out 
of order, and is expensive of repair. Eutherford’s minimum 
thermometer is a spirit one, with the tube horizontal. The 
spirit, in sinking by a depressure of temperature, draws the 
index with it, but when a rise occurs the index remains behind, 
and its end, farthest from the bulb, shows the greatest depres- 
sion since the previous observation. The instrument is set for 
further use by a gentle tap, which brings the index to the top 
of the column of spirit, wherever that may happen to be. In 
Phillip’s maximum thermometer a small portion of the mercury 
is separated from the bulk by a bubble of air. When the tem- 
perature rises, this detached portion is pushed forwards, but 
when the temperature falls, it does not recede with the main 
body; consequently it marks the maximum temperature that has 
occurred since the previous observation. 
Concerning simple non-registering thermometers, I need do 
no more than give some tests for them, using the words of an 
eminent living physicist and chemist. “When immersed in 
melting ice, the column of mercury should indicate exactly 
32° F. ; when suspended with its scale immersed in the steam 
of water boiling in a metal vessel, the barometer standing at 30 
inches [the place of observation being at the level of the sea], 
the mercury should remain stationary at 212°. When the 
instrument is inverted, the mercury should fill the tube, and 
fall with a metallic click, thus showing the perfect exclusion of 
air. The value of the degrees throughout the tube should be 
uniform. To ascertain this, a little cylinder of mercury may be 
detached from the column by a slight jerk, and on inclining the 
tube it may be made to pass from one portion of the bore to 
another. If the scale be properly graduated, the column will 
occupy an equal number of degrees in all parts of the tube.” 
Thermometers should be hung on a proper stand, facing the 
north and protected behind and laterally from the direct rays of 
the sun, yet not so as to impede the free access of air. 
Thermometers of a certain sort can be obtained for a shilling, 
but I need hardly say, these are philosophical toys rather than 
meteorological instruments. Let the amateur beware of them. 
A good observatory thermometer costs at least fifteen shillings, 
