REPORT ON METEOROLOGY. 
209 
mercury from the end of the tube*,—a proposal made, in the 
middle of the last century, by Lord Charles Cavendish, and 
since that revived by Mr. Blackadderf. I have elsewhere taken 
occasion to point out the principal defects to which it is liable J. 
In connexion with the thermometer we must mention an ele¬ 
gant method devised by M. Bessel of finding the correction 
to be applied to any thermometer on account of inequalities in 
the bore ; which consists in breaking off' columns of various 
lengths of mercury in the tube, causing them successively to 
traverse the length of the scale ; and by noting the spaces 
occupied by each at the different points, an equation for the 
scale of the particular instrument may be formed §. 
A very interesting discovery has recently been made with 
regard to the early history of the thermometer, by Signor 
Libri of Florence ||. In 1829 were found at Florence a large 
number of the original alcoholic thermometers made under 
the direction of the Academia del Cimento, which enabled Sig. 
Libri to restore the true scale of these early instruments so as 
to afford a direct comparison with those of modern times. The 
scale was divided into 50 degrees. The zero corresponded 
to—15° of Reaumur, the 50th degree with 44° R; and it 
stood at 13^° in melting ice. The latter fact is interesting 
because it shows that no sensible change had taken place in 
the freezing point of those instruments during the lapse of 
nearly two centuries ; for it is recorded that in melting ice the 
liquid marked 1 3\°. It is well known that, from whatever cause, 
many old thermometers indicate a temperature somewhat above 
32° Fahr. when plunged in melting ice. In some cases however 
the change has not been noticed, and this is one of the most 
remarkable examples. Some years ago the question excited 
considerable discussion ; but as nothing has been added to 
our knowledge for some time, I shall merely refer in a note to 
the papers which have treated of it ^[. By an accident almost 
as fortunate as the recovery of the thermometers, some regi¬ 
sters nearly complete for sixteen years and kept by Raineri, a 
pupil of Galileo, have come to light; and by the discussion of 
them, with a knowledge of the true scale, Signor Libri has been 
* Poggendorff’s Annalen , xxii. 146. f Edinburgh Transactions, vol. x. 
t Edinburgh Journal of Science , ix. 300. 
§ Poggendorff’s Annalen , 1826. Also Bulletin des Sciences Mathematiques, 
viii. 42. and Philosophical Magazine, vol. Ixiii. 
|| Annales de Chimie, xlv. 354. 
Flaugergues, Bibliotheque Universelle , xx. 117, xxi. 252. De la Rive and 
Marcet, Ibid. Avr. 1823. Bellani, Giornale di Fisica, v. Arago, Annales de 
Chimie, xxxii. Moll, Edinburgh Philosophical Journal, ix. 196. 
O 
