



210 Application of the Galvanic Circuit 



Instead of a proportional compass we may use a graduated 

 scale of some translucent substance laid on the printed register. 

 For the sake of uniformity of hygrometric expansion, a gradua- 

 ted scale made of a portion of the registering fillet will perhaps 

 be preferable. A small correction may in this case be applied if 

 necessary, for the rate of the automatic clock on an assumed scale 

 of paper of a second to an inch. A relative rate of two seconds 

 per minute (an improbable occurrence) will on the average cause 

 only an error of one hundredth of a second in reading off by the 



scale. 



All that I have now proposed may be accomplished by the first 

 disk or toothed wheel and tilt hammer. 



Dr. Locke's mode of distinguishing the subdivisions of minutes 



appears to be satisfactory. I see no reason why it may not be 

 effected by a toothed wheel on the arbor of the minute-hand, and 

 another on that of the hour-hand. I mention this for the sake of 

 simplicity, leaving to the mechanician his choice of the mode of 

 effecting the purpose. 



In printing on this automatic clock register, the dates of such 

 events as a series of bisections of a star by the successive wires 

 of a transit instrument placed at equatorial intervals of two sec- 

 onds or more, short blank spaces may be made by dwelling for a 

 very small time with the finger on the break circuit key. 



Isolated events, like the phases of an eclipse or of an occupa- 

 tion, may be distinguished by dwelling with the finger on the 

 key for a space of time longer than the maximum of blank space 

 used in distinguishing the thirty seconds. 



In this way we cannot fail of imprinting the date of an event 

 If the signal break circuit tap occurs in the midst of one of the 

 small blanks, this precaution will secure the record, with an aver- 

 age liability to error for such rare instances, of only one-fourth of 

 the actual blank space of the automatic clock register. 



Washington City, Dec. 15, 1848. 



Having, in the first part of this special report, given a brief 

 history of the steps that led to the invention of the automatic tel- 

 egraph clock, and of its application to Morse's electro-magnetic 

 telegraph, I beg to offer you such suggestions as have occurred to 

 me in relation to the practical application of it to the longitude 

 operations of the coast survey, and to the general purposes of 

 practical astronomy, on which the survey is dependent for the 

 accuracy of its work. 



The great importance of an automatic telegraph clock has 

 often been the subject of conversation between us, but your chief 

 efforts were, necessarily, directed at first to the means of procur- 

 ing it. A hasty glance at the advantages that would result from 

 the certain possession of such an instrument was made by D f - 



