240 /. Locke on the Electro- Chronograph. 



By this invention the observer need not have a clock at his sta- 

 tion — only one clock is necessary. 



15. Letter of Prof. Locke to Lieutenant Maury, Director of 

 the National Observatory, Washington, D. C, dated Cincin- 

 nati, Dec. 13, 1848. 



I enclose to you a specimen of my late invention, the tele- 

 graphic-clock for longitude, (now called the electro-chronograph.) 

 The clock breaks and closes the circuit in such a manner that 

 the seconds are registered in lines about half an inch long, 

 with short breaks between them. This is done without any in- 

 terference with the pendulum. To indicate the minute zero, a 

 break is omitted when two lines run into one, about one inch 

 long. 



Every five minutes, a long line (three seconds) follows the 

 minute zero. Of course the five minutes terminates at the minute 

 zero. Every hour a similar dash p recedes the minute zero, each 

 of these dashes is separated from the minute zero by a few dis- 

 tinct seconds. At the commencement of an hour the three signals 

 come together thus : 



Hour Minute Five Minute ^, 



signal. zero. 8 ignai. Observation. 



Star transits are marked by blanks or breaks made by a finger 

 key under the hand of the observer, (see specimen.) The com- 

 mencement of the break is the punctum of time of the observa- 

 tion. As this may happen between the little breaks between 

 seconds, and be thus a little (one-tenth second) indefinite, I have 

 invented a key which shall measure the breaks and make either 

 end available. By scale and dividers these breaks can be meas- 

 ured to hundredths of a second. The use of such a clock to de- 

 termine longitude on a telegraphic line is evident. It occurred 

 to me that it might also be useful in a local observatory as a faith- 

 ful and convenient register of observations, and especially as it 

 subdivides seconds very accurately. It would relieve the observer 

 from ocular and auricular clock trouble, which when there is a 

 noise about you is often vexatious. The observer has only to 

 watch the transit and press the key at every wire, without ever 

 taking his eye from his telescope. If not used as a substitute for 

 usual clock readings, it might be a convenient check and auxil- 

 iary. If it is thought that it will be useful, it has been proposed 

 that two such clocks be made by our government, one for your 

 Observatory and the other for the Coast Survey. The operation 

 of my clock is as perfect as I could wish, so far as I have 

 observed, and the machinery does not appear to interfere with 

 its rate. 



Mostly, in the observations, the hour and five minute signals 

 would be of little or no use. and might be thrown out of action. 



