1820.] Bonaparte's Fly Bridge at Antwerp. 273 



The above estimate amounting to the sum of 3,622/. 10s. is of 

 course to be considered as a very general statement, for every 

 estimate of this kind must vary according to the position of 

 things. This, however, appears but small, compared with what 

 would be necessary for the erection of a bridge either of iron or 

 stone of 500 yards" in length ; while such a mode of crossing a 

 laro-e river is not only expeditious, but is safe and commodious. 

 Horses and carriases can also lie conveyed by this means with- 

 out unyoking, and passengers may either remam upon deck, or 

 retire into cabins below. For cattle ferries this would be an 

 improvement of much consequence, as almost any number of 

 cattle may be carried across at one operation. 



But establishments of this kind may be required upon a stiU 

 larger scale than is necessary for crossing the Scheldt, the 

 Rhine, and the Po ; and as it is believed that such an idea has 

 not been put in practice in this country, it will be an easy matter 

 to make the trial on any river, or ferry, at a small expense, it 

 being only necessary to apply the ordinary tackle and materials 

 of shipping for making the experiment. 



I am, dear Sir, yours truly, 



Robert Stevenson. 



Article IV. 



Experiments on 'the Effect of a Current of Electricity on the 

 Magnetic Needle.* By John Christian Oersted, Knight of the 

 Order of Danneborg, Professor of Natural Philosophy, and 

 Secretary to the Royal Society of Copenhagen, 



The first experiments respecting the subject which I mean at 

 present to explain, were made by me last winter, while lecturing 

 on electricity, galvanism, and magnetism, in the University. It 

 seemed demonstrated by these experiments that the magnetic 

 needle was moved from its position by the galvanic apparatus, 

 but that the galvanic circle must be complete, and not open, 

 which last method was tried in vain some years ago by very 

 celebrated philosophers. But as these experiments were made 

 with a feeble apparatus, and were not, therefore, sufficiently 

 conclusive, considering the importance of the subject, 1 asso- 

 ciated myself with my friend Esmarck to repeat and extend them 

 by means of a very powerful galvanic battery, provided by us in 

 common. Mr. Wleugel, a Knight of the Order of Danneborg, 

 and at the head of the Pilots, was present at, and assisted in, 

 the experiments. There were present likewise Mr. Hauch, a 

 man very well skilled in the Natural Sciences, Mr. Reinhardt, 



• Trnnilated from a prinird acrount drawn up in Laiin bv the author, and 

 Iransinitted by him to the Kditor of the Annuh of Philosoihy. 



Vol. XVI. N'' IV, S 



