SiniERICAL ELEMENTS OF CRYSTALS. 
201 
negative wire ) or in the interval between both ; it was always 
driven by the discharge nearly perpendicularly upwards to the 
height of twenty or thirty inches j and sometimes descended 
at a very small, and sometimes at a considerable distance, from 
whence i l was projected. When two pith-balls are placed in 
contact with each other in any part of the interval, they are 
likewise driven upwards, and often separates! by the discharge, 
sometimes falling at a small distance from each other, and at 
other times at a greater distance on opposite sides of the 
table. 
1 am. 
Sir, 
Your obliged Servant, 
THOMAS HOWLDY. 
Hertford, 
IDctober \Qth, 1813. 
VI. 
the elementary Particles of certain Crystals: Wil- 
liam Hydb Wollaston, A/. D. Sec. li. S. From the Phi- 
losophical Transactions for 1813. 
A MONO the known forms of crystallized hixlies, there is 
/r^ . L 1 1 WlietlicT the 
tc no one common to a greater number ot substances than rccular octo- 
Sie regular octohedron, and no one in which a correstxmdinor hedron or te- 
r 3 tialiC'dron be 
irfficulty has occurred with regard to determining which mo- Uie pi-iniitive. 
ticaiion of its form is to be considered as primitive ; since, 
I all these substances, the tetrahedron appears to have equal 
t aim to be received as the original from which all their other 
I oditications are to be derived. 
'The relations of these solids to each other is most distinctly 
uhibited to those who are not much conver-iant with crystal- 
.graphy, by assuming the tetrahedron as primitive, for this 
lay immediately be converted into an octohedron by the 
imoval of four smaller tetrahedrons from its solid angles, 
ijg. 1.) 
