Abbe Hauy’s Observations on Double Refraction. 151 
Hatty's Table of Crystals with Single R fraction. 
Fluate of Lime. Amphigene. 
Phosphate of Lime , Tourmaline . 
Telesie . Axinite. 
Spinel le, Disthene. 
5 Garnet. Sulphuret of Zinc. 
In his article on the Double Refraction of Iceland Spar, Haiiy 
gives a detailed account of various experiments, that possess no 
very particular interest. He demonstrates by experiment the error 
of Newton’s law, which we have already mentioned. (See this 
Journal , vol. iv. p. 129.) He establishes the truth of the Huy- 
genian law ; but erroneously remarks, that it accords with ob- 
servations only within certain limits, and he adopts the physi- 
cal hypothesis of Newton, that the particles of light have two 
kinds of poles, on which the Iceland spar exerts a particular ac- 
tion, whose centre is placed in the region of the small solid 
angle of the crystal. 
Observations on Hatty's Experiments. 
The only observations which we have to offer on the prece- 
ding articles, relates to the remark, that the cubical octahedral, 
and rhomboido-dodecahedral crystals have single refraction. The 
only meaning which can be attached to this remark is, that some 
of these bodies have single refraction, for out of the ten crystals 
which Haiiy gives as having only single refraction, there are no 
fewer than six which belong to none of the above primitive 
forms, viz. those marked in Italics at the top of this page. 
The absolute incompatibility of Haiiy’s conclusions with his 
own facts, will appear still more strikingly from his list of tran- 
sparent crystals, which have the cube for their primitive form, 
viz. 
Boracite , Analcime , 
Muriate of Soda, Scheelin calcaire* 
Amphigene , Oxide of Tin , 
every one of which, with the single exception of Muriate of 
Soda , has double refraction. 
Believing, therefore, that all these five crystals had no double 
refraction, when they actually possessed it, Haiiy deduced the 
conclusion, that all cubical crystals had single refraction, where- 
as this property belonged only to one out of six. The conclu- 
