12 REPORT—1863. 
selves in a line with the light and the shadow of our body, we are surprised to find 
that the light and the shadow seem not to be connected at all, and that, instead of 
being in a line, they appear bent to an angle of 160° instead of forming one of 180°; 
so that we see both the light and the shadow a little before us, where they are not 
expected to be. The eye refracts the line formed by the ray of light and that formed 
by the shadow, and the efiect is like that of the stick, one-half of which, being im- 
mersed in water, appears crooked, or bent into an angle at the point of immersion. 
This enlargement of the field of vision to an angle of 200° is one of those innu- 
merable and wonderful resources of nature by which the beauty of the effect is in- 
creased. By it our attention is called to the various parts of the panorama which 
appear in any way a desirable point of observation, and we are warned of any 
danger from objects coming to us in the most oblique direction. These advantages 
are particularly felt in our crowded towns, where we are obliged to be constantly 
on the lookout for all that is passing around us. 
On Specific Refractive Energy. 
By J. H. Guanstonez, Ph.D., F.R.S., and Rey. T, P. Darz, MA., FRAN. 
In a paper laid before the Royal Society a few months ago, the authors came to 
the conclusion that every liquid is endowed with a certain optical property, which 
is independent of its temperature, and which accompanies the substance in its 
mixtures with other liquids, and to a certain extent in its chemical combinations. 
This property is the refractive index, minus unity, divided by the density 
=C,and for this constant the authors have suggested the term ‘specific refractive 
energy.’ It is not maintained that the above formula represents the property with per- 
fect accuracy, for each observed refractive index is affected by dispersion, which does 
not follow the same law; and evenif the refraction of the theoretical limit of the 
spectrum be taken,” , there is apparently some disturbing cause of a higher order 
which still remains unaccounted for. Other physicists have sought for this property 
in what Newton called the absolute refractive power, — , but this does not agree 
80 well with the experimental observations. 
The authors now proposed to show how nearly the expression aa represents 
the real law as determined from observation, and under what varied circumstances 
it may be applied, and also to suggest a possible cause of its divergence from abso- 
lute coincidence. In doing so they referred not merely to experiments of their own, 
but also to those of Dulong, Jamin, and Le Roux on the refraction of gases and 
Mes ae and to other determinations by Brewster, Deville, Weiss, and Schraub. 
. Specific refractive energy and change of volume by heat.—It was shown in 
the paper above referred to that the specific refractive energy of a liquid, a D ” (or if 
. malas 
y represent the theoretical limit of the index, ae, is a constant, or very nearly 80, 
at all temperatures. Yet in almost every instance examined it was found that the 
specific refractive energy slightly diminished as the temperature increased. The 
exceptions are quite within the limits of errors of experiment, and may probably be 
thus accounted for. 
2. Specific refractive energy and change of volume by pressure.—The single experi- 
ment on this subject made by Jamin on water gaye a result which is about equally 
accordant with theory, whether, with that observer, we calculate it by DD - or 
—l 
prefer the formula — 
3. Specific refractive energy and change of aggregate condition.—It has been shown 
in previous papers that the refractive energies of water and phosphorus in the liquid 
