for computing local Attraction. 359 



the island of Ascension, while she would suppose herself in ner 

 lect safety. ""^ 



Enough has now been said to prove that the principle upon 

 which this table is constructed must necessarily be erroneous 

 and we hope it may be the means of preventing any further issue 

 ot the copies of it; for we must not consider an error of this 

 kind in the light of a mere philosophical inaccuracv, but as one 

 which may involve in it the destruction of lives and property to 

 an immense extent. I make no pretensions to scrutinize the ma 

 thematical introduction to the table in question, I have every 

 respect for the mathematical talents of its learned author, and 

 have httle doubt this part is correct; it is however highly pro- 

 bable that the error is in the data or h^■pothesis. It is certainly 

 very improbable that iron at the equator should lose all its effect 

 on a magnetised needle, as supposed by Captain Flinders; but it 

 IS actually impossible that the change should be such as is indi- 

 cated in the table before us. 



I shall make only one other observation, which is, that an error 

 once introduced into nautical computations is extremely difficult 

 to eradicate. The midshipman who learns the use of Dn Youn<v's 

 table this year will use it all his life, and with the utmost con- 

 hdence, from the authority and weight which the sanction of the 

 Board of Longitude very properly has with men in the nautical 

 profession; a circumstance, however, which renders it the more 

 imperiously necessary that all the remaining copies of this table 

 should be destroyed. Yours, &c. 



_. Nauticus. 



LX. On the Alteration ivMch S?dphuric Acid experiences in 



acting ttpon Alcohol *■ 



[Concluded from p. 2y5.] 



I' !' T the GOth volume, p. 54, of the Anna/en der Phvsik, 

 September 1 8 18, that the memoir of M. Sertuerner is to be foiind 



alcohol to form ether, produces three acids, which he desi-.uues 

 by the names of acidum prolcenothiomcum, acidum deuiccno- 

 Ifiwnuum, acidum trttoenolhionicum. The following is the man- 

 ner in which the first of these acids is obtained. Equal parts of 

 sulphuric acid, and of pure, or at least very concentrated, alcohol 

 are mixed together; the mixture is heated, and when saturated 

 with chalk, as soon as ,t is a little reduced, sulphate of lime is form- 

 ed, which IS separated from the liquid bv filtration and prcssinir. 

 On evaporating the liquid by a slow heat, and filtering it at tlie 

 • I-'roiu Ann. dc Chim'ic, Jan. 1820. 



nioincnt 



