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POPULAR SCIENCE REVIEW. 
Polarisation of Light by Sugar : a Peculiar Effect. — M. Maumen6 has 
described to the French Academy fee (“ The Academy,” July 24) a series 
of experiments on inverted sugar, so called from its action on polarised 
light. Cane sugar consisting of C 12 H 22 O n is crystallisable, and produces 
a right-handed rotation of polarised light. Inverted sugar stated to be com- 
posed of C 6 H 12 0 6 is not crystallisable, and gives a left-handed rotation. 
M. Maumene finds inverted sugar has no constant composition, but is a 
mixture of various proportions of glycose, chylariose, and neutral sugar. 
Acting upon very white Narbonne honey with alcohol of 90°, then cooling 
the solution to near zero C., separating a heavy layer, adding water and 
filtering, gives a fluid which is easy to examine with a saccharometer and 
marks zero — it contains neutral sugar. Acting upon this sugar with lime 
water, passing through it a current of carbonic acid, which occasions a pure 
blue precipitate of carbonate of lime, and filtering, affords a solution that 
gives a right-handed rotation of 8° to 10°. The substance left on the filter 
was divided into two parts, and to one water was added, dissolving the chy- 
lariose and giving a very white precipitate of carbonate of lime. The clear 
fluid produced a left-handed rotation of 5°, equal to 47° - o for a volume of 
100. The insoluble matter diffused through water carbonated and filtered 
showed 13° left rotation, or 91° for a volume of 100. M. Maumene adds 
that inverted sugar burns much more readily than common sugar — a fact of 
importance in analysis when the quantity of ash has to be ascertained. 
Spectra of Stars. — It appears that the late Professor d’Arrest had con- 
cluded the observations on this point before his death. The conclusions he 
arrives at are : (1) that the third type of spectrum (channelled spaces) is 
not exclusively confined to orange or red stars, and that several deep-hued 
orange stars give an ordinary spectrum. Perception of colour (especially 
red) depends so much on the eye of the observer that Professor d’Arrest’s 
result must be taken rather as a caution against a hasty generalisation than 
as disproving any connexion between colour and the nature of the spectrum ; 
(2) that the fourth type of spectrum is much more closely connected with 
deep orange or red stars, and that the bands in this spectrum may be re- 
solved into a number of fine lines ; (3) that as a rule such striking spectra 
accompany variability in a star ; (4) that no general difference can be traced 
between the spectra of stars in one part of the heavens and of those in 
another, so that there is no truth in the assertion that the red and yellow 
are wanting in all the stars of Orion. 
Propelling Ships by Utilising the Action of Waves. — A paper of great in- 
terest is that read before the British Association by Mr. Beuachamp Tower, 
who described a contrivance for obtaining motive power from wave-motion. 
A heavy weight, supported upon springs, vibrates in periods of the same 
length as the wave-periods. By means of gearing the motive power obtained 
from the rising and falling of'the weight is made to propel the vessel. 
New Property of Aluminum. — M. E. Ducretet observes [“ Journ. de 
Phys.” iv. 84] that on inserting in a galvanic circuit a voltameter with two 
electrodes, one of aluminum, the other of platinum, different effects are ob- 
tained according to the direction of the current. When the aluminum re- 
ceives the negative electricity the water is decomposed and the current 
traverses the circuit freely. But on reversing the current the decomposition 
