Contributions to Physiological Technique 365 



sation.i Of course it is impossible to give Signals 1, 2, and 3 simultane- 

 ously, but if it be necessary to signal the simultaneous occurrence of two 

 events, this can be indicated by Signal 3, the separate events being 

 indicated by Signals 1 and 2. 



The connections of fig. 4, A, are not the only ones possible to attain 

 the end in view, and in fact are not applicable to the Brodie- 

 Palmer clock on account of the permanent connection in that 

 apparatus of one battery-pole with one side of the clock-contact. 

 Altogether there are four modes of arranging the connections 

 possible according to whether the continuous closure of the circuit 

 independently of the clock in Signal 2 is effected (a) by the 

 " switch " or (6) by the " key " ; and in each of these cases 

 whether the clock-contact is put in permanent connection (ac, he) 

 with the battery or {ad, hd) with the signal. These four different 

 possible arrangements will now be referred to as ac, he, ad, and 

 hd respectively. It is unnecessary to describe them in detail 

 systematically ; they may be easily worked out by those inter- 

 ested. 



The arrangement of connections in fig. 4, A, corresponds with ad. 

 This is theoretically the most preferable of the four, because short- 

 circuiting of the battery is only made use of in Signal 3. With 

 the arrangement hd short-circuiting is continuous during Signal 1. 

 It is therefore best avoided. With the arrangement ac short- 

 circuiting of the battery tends to be, and with the arrangement 

 he is certainly, produced during Signal 1, but only during the clock- 

 contact closures, and is therefore practically negligible. Both of 

 these arrangements can therefore be used with the Brodie-Palmer 

 clock, and the way of connecting it up in the arrangement axi is 

 shown specially in fig. 5. 



In order to ensure that the short-circuiting of the electromagnet of 

 the chronograph effectively demagnetises it for the production of 

 Signal 3, sufficient strength must be given to the armature-spring, 

 and actual contact of the armature with the poles must in some 

 cases be prevented, best by a screw adjustment, but extern 

 poraneously by paper or other material intervening. An absence 

 of inertial overthrow of the writing-lever is also desirable for 

 Signal 3, which is not given in fig. 3 as well as it can be got with 

 a more suitable form of signal than that actually used. 

 If it be only desired to give Signal 3 — the advantage of which is, of 

 course, that there is no temporary loss of time-record — there can be 



Any risk of unipolar excitation by the extra-current of the chronographic electro- 

 magnet may be avoided by connecting up in parallel with the clock-contact an electrolytic 

 "spark-trap" consisting of aluminium electrodes in a solution of sodium sulphate 

 (ct Ostwald-Luther, Physiko-chemische Messungen, 1902, p. 397). This should, in fact, 

 be in permanent use with the clock if only to prolong the life of the contact. 



