14 
7 
urements obtained with it represent the first experimental 
data that have ever been obtained in this field of electric 
research. 
to 
ApparATUuS for studying the magnetic lag in closed magnetic 
circuits and diagrams, plotted from experimental data, 
recording the results obtained. Exhibited by Chas. T. 
Rittenhouse, Fellow in Electricity, Columbia University. 
When iron is magnetized by a rapidly varying force 
the magnetization does not keep in step with the force, but 
lags behindit. This lag is due to induced currents in the 
mass of the iron and to internal viscosity; it is especially 
strong in closed magnetic circuits, and increases with the 
increase of the speed of the magnetizing force, but dimin- 
ishes with the increase of temperature. 
3. APPARATUS employed for generating the radiant energy dis- 
covered by Professor Réntgen. Exhibited by Prof. M. 
I) Popir. 
A rotating current interruptor and induction coil and 
different types of Crooke’s and electrodeless tubes. 
4. SILHOUETTES or RapioGRAPHS obtained by the Rontgen 
method. Exhibited by several physicists whose names 
are attached to the several exhibits. 
CHEMISTRY. 
1 
In CHARGE oF C. E. PELLEW AND Morris LOEB. 
rt. ArRGon AND Hetium. Exhibited by Charles E. Pellew and 
Samuel A. Tucker. 
Argon and Helium are two newly discovered elements 
of the Nitrogen group. Argon occurs in minute particles 
in the atmosphere. ; 
Helium was first discovered by the spectroscope, in the 
atmosphere of the sun, and more recently has been pre- 
pared in bulk from Monazite and other minerals. 
