5. NOTES FROM THE PHYSICAL LABORATORY. 
I. An Instrument for Rapidly Changing the Cell Ar- 
rangement OF Large Batteries. 
(Presented to the Denison Scientific Association, April 5th, 1890.) 
One of the greatest difficulties m the way of the teacher of 
Physics who believes in the thorough application of inductive 
methods, is the great amount of time necessary for the systematic 
development of his subject. This difficulty meets both the lecturer 
and the laboratory director. It happens constantly, for instance, in a 
lecture course on electricity — and not infrequently in courses on other 
branches of physical science — that some question is asked that can be 
satisfactorily answered by even a moment’s use of an electrical current 
of a definite strength and potential. But the demonstrator, not having 
just the right kind of current immediately available and being pressed 
for time, is met by this alternative : he may takp five or ten minutes 
of time that he really needs for the demonstration of a more important 
point, to set up a battery, perhaps at the risk of wearing out the patience of 
his class, or, unwilling to make such a sacrifice, he may content himself 
with the unsatisfactory answer, that if he had time to do so and so, 
such and such a result would be obtained In either case he is likely 
to lose the attention of his class and fail to produce conviction in their 
minds. The laboratory director feels even more keenly than the de- 
monstrator the need of having all the laboratory facilities completely 
and immediately under his control. Many an earnest laboratory stu- 
dent loses interest in his work because he is compelled to waste so 
much time in simply getting ready for each experiment or determina- 
tion that he makes. There is great need of more and better regulat- 
ing devices in physical lecture room and laboratories. The instru- 
ment shown in plan and elevation at the end of this article, Plate B, 
Figs. I and 2 , is designed to supply one need, namely, an electrical 
current easily adapted to a wide variety of uses. It gives at a mo- 
ment’s notice a current of any ampere strength and voltage within a 
considerable range, by changing the arrangement of cells in a large 
