to CORRESPONDENTS. 



The ri)llo\\ ing Coiiiimmicatioiu have been received : 



On AeriiU Navigation. — Mr. Gutteridge on the Measurement of Timber.— 

 On Pillar-work and Way-going-work in Collieries. — Mr.MusHET on the Origin of 

 the Blast Furnace. 



We must decline inserting E's Letter on the controversy respecting Mr. Hera- 

 path's Theory, as it treats only on personal topics of which, no doubt, our readers 

 will tliink they have already had too much. We agree vi-ith E, " that the scientific 

 public have only to do with the Theory itself, and not with individual dispositions 

 and feelings;" and we do not wish to have a controversy prolonged, when it has 

 assumed this character. 



This Day is published, 



TRANSACTIONS of the GEOLOGICAL SOCIETY, PART I. 

 VOLUME I. Second Series : with Twenty-four Platei. Quarto. 

 ll. I 1j. 6(i. 



Muy be had of the Booksellers, and at the House of the Society, 20, 

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Just published, Price 4j. 



THE METHOD OF FINDING THE LONGITUDE AT SEA, 

 by TIME-KEEPERS : to which are added Tables of Equations 

 to Equal Altitudes, more extensive and accurate than any hitherto 

 published. 



By WILLIAM WALES, F.R.S. ' 

 And late Master of the Royal Mathematical School in Christ's Hospital. 

 Fourth Edition, corrected, and enlarged by an Appendix, containing 

 two practical Rules for ascertaining the Longitude by the Lunar Obser- 

 vations; 



By the Rev. JOHN BRINKLEY, D.D. F.R.G. &c. &c. 



The Tables revised, and the Examples brought up to the Year 182S, 



By J. xMARSHALL. 



Printed for J. Collingwood, in the Strand, 



BRIDGES, BRICK, STONE, IRON AND CHAIN. 



TRACTS on VAULTS and BRIDGES; containing Observations 

 on the various Forniij of Viiults, on the taking down and Rebuilding 

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T. and W. Boone have just published A Select List (to be had gratis) 

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