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SCIENTIP^IC INTELLIGENCE. 



NATURAL PiBEILOSOPHY. 



1. Lieutenant Drummond on the means q/' Jacilitating the 

 Observations of Distant Stations on Geodesical Operations. — 

 There was lately read to the Royal Society of London, a paper 

 on the means of facilitating the observations of Distant Stations- 

 in geodesical operations, by a highly accomplished engineer, our 

 friend and former pupil, Lieutenant T. Drummond, Royal En- 

 gineers. A committee of the House of Commons having re- 

 commended to his Majesty's Government, in 1824, the accom- 

 plishment of a new survey of Ireland, the author was entrusted 

 by Lieutenant-Colonel Colby with the contrivance of means for 

 obviating the delay which usually occurs, in connecting the sta- 

 tions in triangulation in this country, from the frequently unfa- 

 vourable state of the weather not permitting the ordinary sig- 

 nals to be seen from distant stations. To remove this inconve- 

 nience, as far as day observations were concerned. Lieutenant 

 Drummond had recourse, in preliminary trials, to tin-plates, as 

 substitutes for regular heliostats ; and the advantages derived, 

 from applying, even in this rough way, the principle of reflec- 

 tion, as suggested by Professor Gauss, led to the invention of an 

 instrument described in the paper, which was used with much 

 benefit last season in the survey of Ireland. It was also desira- 

 ble to have some method of connecting the stations during the 

 night. For this purpose, Bengal and white lights had formerly 

 been employed by General Roy, but the use of them had given 

 way to that of Argand lamps, their light being concentrated, and 

 reflected towards the observers, by a parabolic mirror. These, 

 however, had been found to answer but imperfectly ; and Colo- 

 nel Colby and Captain Kater, when connecting the meridians of 

 Greenwich and Paris, in 1821, with MM. Matthieu and Ara- 

 go, employed the light of an Argand lamp, with four concen- 

 tric wicks, concentrated by a lens. This apparatus, however, 

 u^as found to be, in many respects, objectionable ; and the para- 



