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 Sth, 1890.) 



One of the greatest difficulties in 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 take 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 // 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 Tnere 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, 

 J^i'^s. I and 2, is designed to supjjly 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 

 consideral)le range, by changing the arrangement of cells in a large 



