Royal Astronomical Society. 143 



vanic magnet whose current is interrupted occasionally) upon a fillet 

 of paper, which is drawn by machinery Avith a nearly uniform speed 

 under the style. With this apparatus it is evident that a signal 

 almost instantaneous in duration can be given ; either by supposing 

 the ordinary state of the apparatus to be that of exerting a pressure 

 on the style, and giving the signal by interrupting the galvanic 

 current ; or by supposing that in the ordinary state of the apparatus 

 no pressure is exerted, and that the signal is given by completing 

 the galvanic circuit, which animates the magnet and creates an in- 

 stantaneous pressure. In the first of these forms the record will ex- 

 hibit the appearance of long lines interrupted by very short intervals ; 

 in the second it will have the appearance of punctured dots, with 

 wide spaces between them. Now, as no reliance whatever can be 

 placed on the uniformity of speed of the machinery which draws the 

 fillet, it is necessary to make such connexion of the apparatus with 

 a trustworthy clock, that the seconds (or other uniform intervals) of 

 the clock shall be recorded in the same manner upon the same fillet. 

 If this be effected by the same galvanic communication and the same 

 magnet, then, in the first case (or that in which the ordinary state 

 is that of pressure on the style), the record will consist of an indented 

 line, interrupted at short and sensibly equal intervals corresponding 

 to the seconds marked by the clock, and interrupted also at other 

 points corresponding to those instants at which the observer has, by 

 a voluntary eflfort, interrupted the galvanic circuit in order to give a 

 signal. This is the method adopted by Dr. Locke. In the second 

 case (where in the ordinary state no pressure is exerted), there will 

 be a series of punctured dots at sensibly equal intervals corresponding 

 to the seconds of the clock, and, mingled with these, there will be 

 the dots corresponding to the instants at which the observer has 

 completed the galvanic circuit. This is the method adopted by 

 Professor Mitchell. 



In either of these methods there is no difficulty in producing such 

 a variation, repetition, or omission, of the clock-signals, as will di- 

 stinctly mark the beginnings of minutes, of every five minutes, &c. 



Dr. Locke appears to have been induced to adopt the method of 

 registering by interrupting the circuit (which in its ordinary state 

 was complete), by the following consideration : — His object was to 

 record upon one moving fillet of paper at Cincinnati the observations 

 made at three stations (Louisville, Cincinnati, and Pittsburg), and 

 also the seconds of the clock. He remarked, then, that the interrup- 

 tion of the circuit for any one place would interrupt it for all ; and 

 therefore, at whatever place the signal of observation was made by 

 interruption of circuit, the corresponding interruption would neces- 

 sarily be made in the indented line on the fillet of paper. But he 

 remarked also that the connexion of the parts of the circuit at one 

 place would not effect the connexion for all ; and he appears to have 

 inferred that, if a single wire only were used extending along all the 

 stations, it would be impossible to use it by the method of completing 

 the circuit for signal, and that, in fact, a separate wire would be ne- 

 cessary for each separate station. This inference, as the Astronomer 



