244 J. 8. Cheyney on the Chladni Plates, 
on its axis until the front is horizontal and the “ square prism” _ 
slipped into the front of the objective, so that the light is re 
flected upon the screen. The plate is then focussed, sprinkled — 
with sand, and touched as usual with the bow. 
The sudden appearance of the nodal lines is very beautiful. 
Any figures which can be formed on glass plates can thus be 
shown with great ease to the largest audience. 
The retarding influence of a solution of gum on the sand 
can be shown in action, and the curves studied in detail. 
(2.) “ The Magnetic Phantom” can also be most success 
fully shown in the same way, employing a plate coated withal — 
bumen to prevent the filings sliding too much in a body. Nu 
merous other similar experiments, which will occur to every op — 
erator, can be readily and beautifully performed. | 
(3.) The waves produced by striking the surface of mercury 
in a suitable dish, the colors of thin plates obtained from the 
action of oils upon water, &c., can be readily shown by depress 
ing the front of the lantern, without the object-glasses, ame — 
receiving the light reflected from the dish of fluid upon? 
proper focussing glass and thus upon the screen. | 
_(4) In spectrum analysis, the arrangement gives se 
cility, especially by mounting the prism-box described by a | 
Cooke, Jr.,# so as to slide into the front of the object es 
To keep the edge of the prisms parallel to the slit, a not? 18 
cut in the front of the object tube and a corresponding projec 
tion screwed into the sliding end of the prism-box. re 
6. e arrangement proposed has the advantage ¢ pre | 
plicity, and gives the greatest facility in the use of the Janta 
or ordinary purposes as well as in the class of exp 
described 
Of course the condensers should not be subjected to we 
cal current of hot air from the lime or electric light un here i8 
have been thoroughly warmed. With this precaution * 
* no rr 
T would remark, in conclusion, that this mode of er 
the lantern was devised in the spring, and effected, 1 sil 
essential features, in the autumn of 1867; and has been : 
with great satisfaction in results ever since. . 
Frankford, Philad., Pa, June 25, 1868. 
* This Journal, II, xl, 243, Sept. 1865. 
