HERTZIAN ^YAVE WIRELESS TELEGRAPHY. 199 



varied, so that it is possible to regulate this period without disturbing 

 the number of interruptions per second. 



The sparks obtained from a coil worked with a turbine interrupter 

 have more quantity than the sparks obtained with any other interrupter 

 under similar conditions, and the coil can be worked with a far higher 

 voltage than is possible when using the hammer break. In this manner, 

 the appearance of the secondary sparks can be varied from the thin 

 snappy sparks given by the hammer break to the thick flame-like arc 

 sparks given by the electrolytic break. This break can be adapted 

 for any voltage from twelve to two hundred and fifty volts, and the 

 primary circuit can not be closed before the interrupter is acting. 

 The mercury in the break is generally covered with alcohol or paraffin 

 oil to reduce oxidation, and the appliance is nearly noiseless when in 

 operation. The mercury has to be cleaned at intervals, if the inter- 

 rupter is much used. If alcohol is used to cover the mercury, the 

 cleaning is very simple; the break requires only to be rinsed under a 

 water tap. When paraffin oil is used, the cleaning is generally effected 

 with the help of a few ounces of sulphuric acid in a very few minutes. 

 It is best, however, to clean the mercury continuously by allowing the 

 water to flow over it. 



The motor driving the centrifugal pump and the fan can be wound 

 for any voltage, and it is best to have it so arranged that this motor 

 works on the same battery which supplies the primary circuit of the 

 coil, the two circuits working parallel together, A rheostat can be 

 added to the motor circuit to regulate the speed. 



The turbine break driven by an independent motor, which is kept 

 always running, has another advantage over the hammer break in 

 practical wireless telegraphy, viz., that a useful secondary spark can be 

 secured with a shorter time of closure of the primary circuit, since there 

 is no inertia to overcome as in the case of the hammer break. This 

 latter form has only continued in use because of its simplicity and ease 

 of management by ordinary operators. 



The mercury turbine interrupter has been extensively adopted both 

 in the German and British navies in connection with induction coils 

 used for wireless telegraphy. 



Lastly we have the electrolytic interrupters, the first of which was 

 introduced by Dr. Wehnelt, of Charlottenburg, in the year 1899, and 

 modified by subsequent inventors. In its original form, a glass vessel 

 filled with dilute sulphuric acid (one of acid to five or else ten parts 

 of water) contains two electrodes of very different sizes; one is a large 

 lead electrode formed of a piece of sheet lead laid round the interior 

 of the vessel, and the other is a short piece of platinum wire projecting 

 from the end of a glass or porcelain tube. The smaller of these elec- 



