ISO Eeccaria’^s- HwpC'rlmeoiis on ’DmM& Refraction. 
exactly than Ba;rtholinus, there is- reason to believe that he 
made some experiments on the subject, which confirmed those 
of Huygens; and yet it is strange,, thatj without assigning any 
reasons, he should reject Huygens'^s law, and substitute another^ 
entirely inconsistent with the very experinients he has praised* 
Unaccountable as this is, it is by lio means iminstructive, and 
holds out a useful lesson to the vain admirers- of human genius* 
Tn his speculations respecting the cause of the disappearance 
and reappearance of the pencil, when light is transmitted through 
two rhombs of calcareous-spar, Newton has been more fortunate; 
and he has undoubtedly the merit of having first suggested the 
idea of the polarity of light, and of having ascribed the pheno- 
mena of the polarisation of the pencils in Iceland-spar to origi- 
nal properties possessed by different sides of the rays. 
Sect. II. — Account of the Experiments of Beccaria. 
A paper, etitkled, An Account of the Double Refractions 
in Crystals f by Father John Beccaria, Professor of Experi- 
mental Philosophy at Turin, was read before the Royal Society 
of London on the 18th March 176S, and printed in the Trans- 
actions for that year, vol. lii. p. 486. The principal result of 
these experiments is, that the double refraction in rock-crystal 
is greatest when the ray is perpendicular to the axis of the crys- 
tal, and that the images approached to coincidence as the ray 
approached to that axis. This conclusion must be considered 
as of some importance, as it overturns the peculiar law of double 
refraction which Huygens had devised for rock-crystal alone, 
(see Vol. HI. p. 28.) According to this law, the double refrac- 
tion of rock-crystal should be the same in every direction; where- 
as Beccaria has proved that it diminishes as the ray approaches 
to the axis. 
Beccaria’s paper is concluded with some unimportant queries, 
in one of which he conjectures, that the examination of the 
double refraction of different crystals may lead to the determi- 
nation of their structure and mode of formation. 
( To be continued.) 
