148 On the Application of Galvanic Electricity 



sufficiently powerful to work the register magnet. The oxydi- 

 zation would give rise to imperfect contact^ and the necessity 

 of frequently disturbing the clock works in order to re-polish 

 the springs^ which of course should be avoided if possible. 



The operation of the clock circuit y,dll now be readily un- 

 derstood. The '^contact" being made every second by the 

 clock itself, the current from the one-celled battery causes 

 the relay magnet to attract its armature, thus bringing the 

 tAvo platinum points of the relay before mentioned into con- 

 tact ; the contact completes the circuit from the battery to 

 the clock register, whose magnet immediately attracts the 

 armature and lever, causing the style to indent the paper. 

 This action being repeated every second, coincidently with the 

 oscillations of the clock pendulum, if the paper be put in 

 motion, a series of dots about an inch apart is made on it as 

 it passes through the rollers, every sixtieth dot being left out 

 by reason of the short tooth in the extra wheel, this serving 

 to mark the commencement of each minute. 



The following is the mode of observing with this instrument, 

 as practised in our Observatory : — 



After seeing that the circuits are complete, the register and 

 relay in good adjustment, and the seconds' dotsbeing plainly in- 

 dented on the paper, the observer proceeds to make his observa- 

 tion. Let it be, for instance, the transit of a star over the wires 

 of his transit instrument : — The instrument being in position, 

 and the observer seated at the transit instrument, he watches 

 for the stars' approach to the first wire; when near it, he re- 

 leases the detent of the clock train of the register, and the 

 paper commences to move through the rollers indented at 

 each second by the clock circuit. Immediately the star ap- 

 pears behind the wire, he touches the key for an instant, and 

 the style of the observing circuit indents the paper ; he does 

 this for each wire, until the observation is complete, when he 

 stops the chronograph — always taking care before he stops it 

 that a minute space has occurred on the paper during the 

 observation, in order that the seconds may be dated; if it has 

 not, he must let it run till one occurs ; and it is usual to mark 

 this space with the number of the minute at once, to facilitate 

 '' reading off," as well as to indicate by a number or symbol 

 the object observed. Of course, if several observations are 

 being made in quick succession, the instrument is not stopped 

 till the series is complete. 



It is the custom at the Observatory to " read off'^ every 

 morning, unless the result of any observation be required at 



