188 | “BEMSICES, 
necessity of constantly observing the instruments. The self-register 
invented by Rutherford consisted of two thermometers in the same frame, 
with their tubes horizontal, one of these being filled with mercury, the other 
with colored alcohol. In the tube of the former is a cylindrical steel pin, 
which is pushed forwards by the expansion of the mercury, but does not 
return with its contraction, thus registering the highest temperature. In_ 
the tube of the alcohol thermometer is a fine glass rod, somewhat thicker at 
the extremities, which retains its place when the liquor expands, but is 
retracted with the latter on its contraction by a diminution of the 
temperature. The bulbs of the two thermometers lie in opposite directions 
on the stand. To adjust the apparatus for a fresh experiment it is to be 
gently inclined, the alcohol bulb uppermost, and slightly tapped. The 
steel pin slides down to the top of the mercury, and the glass rod to the end 
of the column of spirit. These indexes are now so placed that an increase 
of temperature causes the steel to advance, its diminution producing the 
retraction of the glass. This instrument is not well calculated for 
travellers, being principally adapted to fixed stations, and is quite 
inapplicable to ascertaining the maxima and minima of temperature in 
mines, caves, Artesian wells, depths at sea, &c. The description of such 
an instrument, invented by Magnus, and called the geothermometer, will be 
found under the head of Mining. 
The mean temperature of the month is obtained by taking the mean of 
all the mean daily temperatures; and that of the year will id the mean of 
the mean monthly temperatures. The maximum of cold occurs about the 
14th of January; that of heat about the 26th of July. The mean annual 
temperature is experienced about April 24th and October 21st. At Paris, 
during the interval from 1665 to 1823, the coldest day fell principally in the 
second half of January. At Frankfort on the Maine, the average of twenty 
years’ observations gave January 15th as the coldest and July 22d as the 
warmest days, the days of mean annual temperature occurring about April 
8th and October 18th. In the torrid zone there are two maxima and two 
minima in each year. The former occur at the equator about April 20th and - 
October 20th; the latter about January 20th and July 20th. The observed 
maxima and minima differ in Surinam by 52°, in Pondicherry by 73°, and 
in Cairo by 88°F. This difference, again, is at Rome 111°, at Paris 142°, 
at Prague 145°, at Moscow 159° at St. Petersburgh 1614°, and in Green- 
land 165°, which agrees with what we have already id on the subject. 
The highest observed temperature in the shade and open air does not 
exceed +113°F".; the minimum is about — 70°F. 
The mean temperature of a place is obtained by taking the mean of as 
many annual means as possible; this may, however, be approximately 
obtained from observations of a few years, the mean annual temperatures of 
a place differing little from each other. Thus, the mean temperature of 
Moscow and St. Petersburgh amounts to 373°—39°F"., of Drontheim to 40°, 
of Stockholm and Christiana to 41°—48°, of Koénigsberg to 434°, of Breslau, 
Dantzig, and Copenhagen, 444° to 451°, of Berlin, Hamburg, and Edinburgh, 
to 461°—48°, of Warsaw. London, Dublin, Prague, and IF'rankfort on the 
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