f 
Physics and Chemistry. ‘ge 
a ice through this film. The water therefore becomes colder and finally 
freezes. This view is adopted by Prof. J. D. Forbes.* Neither Person 
nor rRorbs explain why-a thin film of water in contact with a mass of ice 
has or can have any other temperature than the ice itself, nor why water 
at 0° should give off heat to ice at 0°. Prof. James Thomson’s theoryt 
is in his own words as follows: If to a mass of ice at its melting point, 
tact between small masses of ice. ’ Moreover Farada has shown that 
pressure is Fong ecessary in regelation. Of the numerous experiments 
which he has instituted the following appears to us the most convincing. 
Two round cakes of ice, convex upon the upper surfaces, are placed in water 
ri of hyponitric eid diminishes as the density of the 
The measurements were made with an Oertling’s circle pear phone 
to two ag oe a are i by a filar micrometer in the ocular, to a single 
second, The same phenomenon occurs with the spectrum of <hioraphale 
The stronger the extract in aiken the less is the distance of the 
bands... Thus the absorption-band in the red in the case of a strong 
extract corresponds quite well with Fraunhofer’s ‘tn C; in the case of a 
weak extract it stands at some distance from it. The other absorption- 
bands in this spectrum undergo similar tloations 
These changes in the distances of the dark lines are very sensible even 
in the spectrum of hyponitric acid, wh cae changes in the density of 
the gas are considerable; they are not t however equal for all the dark 
ines, 
Sea ee oa — waalan Bainburgh 
Am Lng adiees — Vou. mee No. = 1861. 
«64 
