THERMOMETRY. 
493 
Notwithstanding that the principles of its construction are 
not of the most exact kind, the instrument invented 
by Sixe in 1782, and thence known as Sixers self- 
registering thermometer, may be pronounced an 
exceedingly useful one, perhaps on the whole the 
best for purely popular purposes, in which portability 
is- not an object. It depends for its action on the un- 
equal expansions of mercury and alcohol, and consists 
of a long glass tube, with bulbs at each end, bent 
twice in the same direction, and to such an extent 
that the three sections resulting from the double 
bending are parallel to each other. Mercury occupies 
the central portions of the tube, and alcohol the two 
ends. The tube is mounted vertically, and the mercury 
is so arranged that it fills those portions of the tube 
adjacent to the lower bend. From the engraving 
a general idea of the instrument will be obtained ; 
it is well known, and further description is not 
requisite. Steel indices slide on each end of the 
mercurial column. 
Another self - registering instrument in general use is 
Rutherford's. This consists really of two thermometers 
placed side by side in a horizontal position, one mercurial 
and the other of spirit. In the former, which registers 
maximum temperatures, is placed a steel index, which is 
pushed forward by the mercury when the temperature rises, 
and remains in that position when the column recedes on the 
temperature falling. In the latter, which registers minimum 
temperatures, there is an index of ivory or glass with a flattened 
end, which recedes with the spirit as it retires in the tube, 
but which, in consequence of its shape, does not return with 
the fluid on an increase of temperature taking place, the spirit 
easily passing by it. It is adjusted to its position at the end 
of the column of spirit by gently shaking the tube with the 
bulb end upwards. The chief drawback in this instrument is 
that occasionally the steel index is found to get clogged by the 
mercury. 
We have now to speak of some single self-registering 
thermometers. 
Professor Phillipses for maximum temperatures, is an im- 
provement on Rutherford's. Here a portion of the mercurial 
column is cut off from the main body by a bubble of air. 
When the temperature rises, the whole column moves 
forward; but on falling, that portion beyond the air-bubble 
remains stationary. The observer can thus at once see the 
extent of the rise. The instrument is set by a gentle tap. 
Negretti and Zambra's maximum self-registering therm o- 
vol. in. — NO. XII. 2 L 
