J. S. Cheyney on the Chiadni Plates. 243 
mined, there is every reason to hope that it may become more 
abundant. Its pyrognostic properties are so very characteristic 
that it may readily be distinguished from any other mineral 
which it resembles in physical characters. In addition to 
fibrous willemite, I have also found chrysotile in fine fibers im- 
bedded in the calcite of Mine Hill; it, however, requires but 
little familiarity with sussexite to distinguish it at a glance 
from these species. 
New Haven, July 18th, 1868. 
Agr. XXIV.—On an easy and very effective mode of showing 
the vibrations in Chladni plates, &c., to a large class, by the 
Tax lantern is constructed as usual, except that the conden- 
8ers project some distance in front of the box, which must no 
be too broad; and the object-glasses are elevated upon a brass 
Stand on the end of a sliding bar two and a half inches wide, 
which slides smoothly and lightly in a groove cut for it under 
bottom of the lantern, and can be clamped in any position 
. . In my earlier experiments, I used a somewhat dif- 
ferent arrangement of the object glasses, but the plan above, 
which is a modification of one devised by Prof. Albert R. Leeds, 
this city, works most satisfactorily. 
The lantern thus constructed, is mounted like the telescope 
ofa theodolite, on an axis turning in a pair of vertical posts, 
Tha tise out of a circular disc of wood 22 inches 1n diameter. 
ay disc is fastened loosely at its center, by a bolt with a screw, 
Ee & ia top of the operating table, and thus can be turned com- 
Pletely round in a horizontal plane, and clamped by the screw 
ere required. 
On one end of the axis of the lantern, and outside of the 
Upright post is a circle of brass 8 inches in diameter, by whic 
by lantern can be clamped at any angle of elevation or depression 
Paha set in a pair of brass clamps on the post. 
bras, Square prism,” (made either solid of glass or hollow of 
= with glass sides and filled with bisulphid of carbon) is 
_ Mounted so that it can be slipped into the front of the object- 
mounting and turned upon an axis as usual. 
-) To show the vibrations in Chladni plates, a narrow clamp, 
fom suitable glass plates, is screwed to the upper part of the 
nt of the lantern, so that the center of the plate is directly 
re the center of the condensers, The lantern is now turned 
a m4 a calcium or electric lantern; by Juss 8. CHEYNEY, — 
