Intelligence and Miscellaneous Articles. 301 



If a wire connected at both extremities with a galvanometer be 

 coiled, in the form of a helix, round a magnet, no current of electricity 

 takes place in it. This is an experiment which has been made by vari- 

 ous persons hundreds of times, in the hope of evolving electricity from 

 magnetism, and, as in other cases in which the wishes of the experi- 

 menter, and the facts, are opposed to each other, has given rise to very 

 conflicting conclusions. But if the magnet be withdrawn from or in- 

 troduced into such a helix, a current of electricity is produced ivhilst 

 the magnet is in motion, and is rendered evident by the deflection of 

 the galvanometer. If a single wire be passed by a magnetic pole, a 

 current of electricity is induced through it which can be rendered 

 sensible. 



Thus is obtained the result so long sought after, — the conversion 

 of magnetism into electricity. Whenever a piece of metal moves near a 

 magnet so as to intersect the magnetic curves, electricity is evolved 

 according to very simple laws. Similar results have been obtained even 

 with the magnetism of the earth ; hut these, and many others, a paper 

 on which has been very recently read before the Royal Society, will 

 be brought forward experimentally on future evenings. 



A powerful electro-magnet constructed by Mr. Marsh of Woolwich 

 was then shown in action j being excited by a rough pair of small 

 plates it supported between 300 and 400 pounds, though before the 

 application of the voltaic power it did not support an ounce. 



XLII. Intelligence and MiscellaJieous Articles. 



ON THE PROBABILITY THAT THE INCRUSTATIONS FROM WHICH 

 MR. WHITE HAS INFERRED THAT THE CEMENT OF WATERLOO 

 BRIDGE IS ILL COMPOUNDED, ARE IN REALITY STALACTITES. 



IN Mr. White's observations on his plans for erecting the New Lon- 

 don Bridge, published in the last Number of the Philosophical 

 Magazine and Annals, he remarks, in page 1S7, that "the ancient 

 buildings in this country as well as in others, sufficiently manifest the 

 indurating nature of lime :" but to this remark the following note is 

 appended : "This may in some measure be doubted, if Waterloo 

 Bridge is to serve as an example ■. for in it the cement or mortar is so 

 ill compounded, as to suffer the lime to escape through the arches, 

 where it forms incrustations on the outside of the stone." 



It occurred to me on perusing these remarks that in all probability 

 the incrustations alluded to by Mr. White were in reality stalactites, 

 and that their formation was due to causes altogether independent of 

 the quality of the cement, and certainly leading to no inference that 

 it is ill compounded. Stalactites are frequently formed in arches and 

 vaults, by a modification of the same process to which they owe their 

 origin in caverns and fissures, the lime they contain being in certain 

 instances derived from the mortar of the structures, and in others, it 

 would seem, from the superincumbent soil. When formed on the sof- 

 fites of the arclies of bridges and similar edifices, they appear to be 

 produced by the drainage through the joints of the masonry of rain- 

 water 



