yg SCIENTIFIC NEWS. 



remain to be accounted for; since Mr. de Prenyls baro- 

 metrical measurement of that height is confirmed by the 

 measurements of Mr. Daune, who had to take the luvels 

 during the construction of the road over it. 



In order to introduce the use of the barometer in geode- 

 tical measurements, undertakea as preliminary operations 

 in planning roads, and particularly for canals that have to 

 traverse heights, wl)ich would be a considerable saving of 

 time and expense, Mr, de Prony has undertaken a series 

 of experiments at Paris and in its vicinity, to ascertain the 

 coefficient best adapted to small heij^hts. lie verifies the 

 barometrical heights by trigonometrical measurements with 

 tke repeating circle. Mr. Mathieu observes at the imperial 

 observatory, and Mr. de Prony at the little observatory 

 constructed for him over the pediment of the House of the 

 Micrometers Legislature. Mr. de Prony employs two micrometers, dia- 

 applicd to the metrically opposite, for adjusting ihe coincidence of the 

 aroeieter. jndex with the tangent to the summit of the mercury, by 

 means of which he makes this adjustment superior in accu- 

 racy to the measuring by the vernier. 



Scarcely a private meeting passes without the class bear- 

 ing some report on new machines or inventions, and on 

 papers subnntted to its examination by persons not yet 

 members. As it is impossible to review all these, I shall 

 only mention : 

 propagation of 1- Researches on the velocity of light, by Mr. Arago, 

 ligli** now member of the class, who has proved, that this velo- 



city is the same„ whether it come directly from the Sun or 

 stars, or from a fire kindled on the Earth, or by reflection 

 from the Earth, a planet, or any terrestrial body, 

 rire-enfiae- ^^* ^^ fire-engine by Mr. Cagniard-Latour, who has mnde 



in it a very happy and inverse application of the screw of 

 Archimedes. 

 Electrochemi- ^" ^^'^ physical d<'partment of the class the most proroi- 

 qtX Inquirir:, nent are the researches of Messrs. Gay-Lussac and Theuard 

 in the brilliant career first opened by Mr« Davy; and 

 though these gentlemen do not appear lo contemplate every 

 fact with the same eyes, the progress of science cannot fail 

 to be promoted by the discassions that arise between 

 thvm. 



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