now measurimj on the Continent. 193 



the time being ascertained with all due care at each of the 

 stations, whatever interruption might take place in the con- 

 tinuity of transmission, from circumstances of weather or other 

 casualties, would be confined in its effect to the spot at which 

 the chain should be broken ; leaving, in such case, the partial 

 determinations, as well as those in which no such interruption 

 should have taken place, available in the general conclusion. 

 Such, in theory, may be considered the most advantageous 

 arrangement. The practical objection to it is : — the number 

 of persons, of competent astronomical qualifications, whom it 

 requires to station simultaneously on different points of the 

 arc. It was the very limited number of such persons that 

 occasioned the successive determinations of the portions of 

 the parallel of 45°, and which rendered the succession a con- 

 sequence of necessity, not of choice. 



Next to the above arrangement, is a second, scarcely infe- 

 rior to it in the certainty, or in the accuracy, of the result, in 

 which the whole line may be covered by the same number of 

 individuals, but having amongst them a smaller proportion of 

 highly qualified observers. It is the mode adopted by the 

 Austrians on their portion of the parallel between Munich and 

 Czernowitz : it consists in deciding, that every alternate observ- 

 ing-station shall be a station of transmission only ; and fur- 

 nishing it accordingly with chronometers, instead of an 

 astronomical clock, and with the more simple apparatus by 

 which the daily rates of chronometers are ascertained, instead 

 of the transit, or repeating circle. The arc is still divided 

 into portions, but these are of greater extent than in the 

 former arrangement, inasmuch as every two stations at which 

 the time is determined, comprehend between them two stations 

 at which signals are given, and a third, intermediate between 

 the two latter, provided with chronometers, and charged to 

 make known the exact interval of time elapsing between the 

 signals on either hand; for which purpose the rates of the 

 chronometers may easily be sufficiently ascertained. If the 

 operations be established along the whole extent of the line at 

 the same period, the astronomical stations may still be cm- 

 ployed, as in the former case, as stations of transmission only, 

 and the total arc be chargeable with the errors only of the 



JAN.— MARCH, 1827. O 



