Proceedings of Learned Societies. 465 



PROCEEDINGS OF LEARNED SOCIETIES. 



BY W. B. TEGETMEIER. 



ROYAL ASTRONOMICAL SOCIETY. 



At the first meeting of the present session, on the 14th Nov., 

 the Astronomer Royal called attention to the efforts which have 

 been lately made to improve onr knowledge of the measure of the 

 earth and of the heavens, his discourse being illustrated by a map 

 showing the triangulation of Europe as it stands at present, and. 

 rendering evident that from the Danube to the North Cape on the 

 N., and to Valentia on the "W., very little is left to be desired. 



Mindful of the past labours of the French and ourselves on the 

 measures of arcs of meridian, the illustrious Struve, the originator 

 of the recent operations, suggested that an arc of parallel should be 

 measured, extending from Valentia, using the present triangulation 

 as far as it reaches, and extending it to the town of Orsk, on the 

 Oural, thus comprising nearly seventy degrees of longitude, an arc 

 of such a length, that, as remarked by the Astronomer Royal, it is 

 scarcely probable that a longer will ever be measured by man. 



For the measure of the earth, then, it was first necessary to find 

 by some lineal measure the length of this arc ; in other words, to find 

 the distance in yards (our standard of measurement) between Va- 

 lentia and Orsk ; and secondly to find the difference in time between 

 the two places. 



First, as to the length of the arc. The British part of it 

 required little attention, as thanks to the admirable work of our 

 Ordnance surveyors, and subsequent investigations by means of 

 chronometers, the actual distance from Valentia to Dover is known 

 to within a few yards. 



Unfortunately the continuation of this line to Paris, which has 

 been effected with equal accuracy, dips too much to the south to 

 be available for the present purpose. It became necessary, therefore, 

 to effect a junction between Dover and Belgium to fill up the gap 

 that there exists between the English and continental systems of 

 triangulation. This has been admirably done by Sir H. James 

 during the present year, and the whole distance from Valentia to 

 some point pretty well advanced, is by this time computed, while 

 the triangulation itself is fast progressing towards Orsk. 



Secondly, as to the difference of local time at the extremities of 

 this arc. This must be determined from those observed at inter- 

 mediate places on the arc; as, for instance, between Valentia and 

 Greenwich, and Greenwich and Brussels, and in this determination 

 telegraphs and railways will be freely used. A complete circuit 

 between the first-named points were placed at Mr. Airy's disposal 

 by Sir Charles Bright, after the Atlantic cable (which " took sea " 

 at Valentia) proved a failure. The difference of time obtained by 

 the electric current (which took l-10th of a second to traverse the 

 800 miles of wire) agreed exactly with that formerly derived from, 

 the transit of chronometers between the two places. 



