Mr. Pictet’s Confederations, &c. 107 
meafurements have not been executed with the very minute 
exadnefs requilite in fo nice and fo important an undertaking. 
The liberal and well conducted operations carried on by the 
Royal Society, under the diredion of the late General Roy, 
for the trigonometrical determination of the diftance between 
the Obfervatories of Greenwich and Paris, render this laft 
fuppofition extremely probable. It now feems evident, that 
the fubftances employed before for the adual meafuiement of 
the bafes muft have been influenced in their length by pyro- 
metrical and hygrometrical effeds, which were either unknown 
or ill-eftimated at that time. The inftruments alfo for obferv- 
ing the celeltial and terreftrial angles were far from the per- 
fection to which they have fince been brought. In a word, the 
whole of the woik Ihould be again undertaken with the far 
greater degree of accuracy which is now within our reach. 
Struck with the importance of thefe fads, I take the liberty 
of tranlmitting to you, Sir, for the confideration of the Royal 
Society, the piefent plan for meafuring, by a commiffion of its 
Members, an arch of the meridian, and of a parallel of longitude, 
having the Obfervatory of Geneva for their common point of 
interfedion. Frequent excurfions in our neighbouring moun- 
tains have convinced me, not only that the meafurement could 
be made, but that it would be perhaps the moft eafily executed 
of any hitherto attempted. The rough Iketch, with its expla- 
nation, joined to the prelent Paper, will give lome account of 
the particulars which I have been able to coiled relative thereto. 
At prefent I fhall only lay before the Society a general furvey 
of the undertaking. 
The belt maps place the town of St. Jean de Maurienne nearly 
fouth of Geneva, at the diftance of about 58 minutes of lati- 
tude. It would be impoflible to extend the meafurement 
P 3 farther 
