Eesoarchcs on the Discharge of the Electric Organ. XI 



a stimulus tlio momentary dimii- 

 lus. Sometimes it was required 

 to experiment with two such 

 momentary stimuh separated by- 



Fig. 4. Momentary stimulus. .^ g|^,^,j-^ interval of time. 



In the direct stimulation (^f the organ, the secondary of the 

 induction coil, the organ and the oscillograph must ho connected 

 in a series. But wlien the discharge is to be photographed, it is 

 necessar}^ to exclude the secondary coil h'om the circuit and to 

 introduce a proper resistance if required. For, if the secondary 

 coil is in the circuit, its enormous self-induction influences and 

 modifies the form of the discharge curve, so that, after a stimulus 

 is given, the exclusion of the secondary coil is necessary. 



To fulfil the requirements above mentioned, a stimulation- 

 apparatus represented in Plate III. and Plate V. was designed. 

 A brief description of the apparatus will l)e given below. 



A small car ^1 liaving three wheels B on each side lies on a 

 pair of cylindrical rails C. The rails have grooves in their upper 

 and lower sides to guide the motion of the wheels. A helical spring 

 is wound round each rail and pushes the car to the left end of the 

 rails. An armature made of laminated iron is fixed to the right 

 end of the car. An electro-magnet fixed on tlie right end of the 

 apparatus, whose core consists of a. l)undle of soft iron wires, 

 attracts the armature and keeps the car at the right end of the 

 rails against the action of the lielical spiings. The current of the 

 electro-magnet flows through tlie I)reaking contrivance of the 

 shutter. When the sliutter is opened (operation a Ix'foi-e men- 

 tioned), the electro-magnet releases the car (operation b) and the 

 latter is jnished away along the rails l)y tlie action of the helical 

 springs. The car has a knocking contrivance on its lower side 

 called a knocher, whose function will ))e explained later on. In 

 order to protect Xho. car from damage caused by a strong collision 

 against the sto]:> at the end of its leftwar<l motion, a special 

 device is attached to the stop. This consists of a pair of jaw's 

 closed by a strong spring. When the car comes against the stop, 

 a plate forming part of the car plunges into the jaws and dissipates 



