M. Arago on the Influence of 'nan- Magnetic Bodies, fyc. 325 



kept at nearly eighteen millions of piastres, without any effect 

 beino- produced on the price of commodities. 



With regard to platinum the case is quite different. As 

 the quantity of this metal, which has only been worked for a 

 short time, is still very inconsiderable, an increase in the pro- 

 duce of the mines which furnish it may bring down greatly 

 its price,— a result which will be extremely fortunate for the 

 useful arts. 



Art. XXIV.— Notice of the recent Researches of M. Arago, 

 on the Influence of Bodies reckoned not magnetic, on the 

 motions of the Magnetic Needle-* 



We have already, in various articles in this work, had occa- 

 sion to lay before our readers an account of M. Arago's mag- 

 netical experiments, and of those of Messrs Barlow, Christie, 

 Babbage, and Herschel, by which they were preceded and 



followed. i « j 



' At the sitting of the Academy of Sciences, held on the <id 

 of July, 1826, M. Arago made a new communication on the 

 subject.' M. Nobili and another Italian natural philosopher, 

 having denied that substances not metallic have any influence 

 on the magnetic oscillations, M. Arago makes the following 



^I Cannot conceive what could have prevented these observers 

 from recognising a fact so easy to verify. In order to show 

 the Academy how impossible it is that I should have been de- 

 ceived, it will be sufficient to state the results at which I have 

 arrived relative to bodies which may be supposed not to con- 

 tain a single metallic particle : for example, distilled water and 



ice. 



With respect to water, the variation between the position 

 of the needle at a very small distance, and at a distance so 

 arcat that the distance of the body may be regarded as no- 

 thing, is in the last case double of what it is in the first. The 

 error of the Italian observers arises perhaps from tins, that 



* This article is partly compose.! of the abstract of the proceeding of the 

 Academy of Scfenc*, published in No*. 84, M, and H7 ot that excellent 

 periodical work I.< Qhbt. 



