192 On the Arcs perpendicular to the Meridian, 



between the French and Austrian portions had been esta- 

 blished under the direction of the intermediate governments. 

 In 1822, the measurement of the corresponding celestial 

 amplitude was commenced by the Austrians, on the portion of 

 the arc comprised between Munich and Buda, in Hungary. 

 The method of determining the celestial amplitude on this 

 parallel was essentially the same as on the arc of the mean 

 parallel ; that is to say, it was accomplished by comparisons of 

 the sidereal time of selected stations, effected by instantaneous 

 signals given at intermediate points. The mode of accom- 

 plishing the comparison, however, and the arrangement of the 

 intermediate signals, differed greatly on all points of this parallel 

 from that pursued on the parallel of 45 degrees : nor were the 

 proceedings upon the French and Austrian portions of the 

 parallel less different from each other in their details of execu- 

 tion, than both were from the proceedings on the other parallel 

 which have been already described. Viewing the subject as 

 interesting alike from its novelty, and from the probability that 

 the method will be frequently and extensively resorted to 

 hereafter, for the determination of differences of longitude, we 

 shall briefly describe the variations which have taken place, 

 and the practical inferences that present experience appears to 

 warrant. Without doubt, theoretically, the most advantageous 

 application of the method of instantaneous signals to the 

 determination of the celestial amplitude corresponding to an 

 arc of considerable extent, would be by the same arrangement 

 of stations as was adopted on the parallel of 45*^ ; namely, the 

 total arc divided into portions by astronomical stations, each 

 provided with a clock, accurately compared with the heavens 

 by astronomical observations, and with each other by signals 

 from one intermediate station, the apparition being registered 

 directly by the clocks ; but in the execution of the operations, 

 it would be preferable, that, instead of the several portions of 

 the arc being determined successively and independently, the 

 whole should be accomplished at the same time, the signals 

 being given and observed along the whole extent of the line on 

 the same nights. By this means no other errors committed in 

 the determination of time, except those at the extremities of 

 the total arc, would influence the ultimate result ; whilst, by 



