378 Analysis of Scientific Books. 



they are worthy of the President of the Royal Society. Of these 

 inquiries the following is a condensed abstract. 



1. Magnetic phenomena are the same, whether electricity is 

 small in quantity and passing through good conductors of con- 

 siderable magnitude ; or whether the conductors are so imper- 

 fect as only to carry a small quantity of electricity ; in both 

 cases the magnetism exhibited is extremely feeble. 



2. Imperfect conducting fluids do not give polarity to steel 

 when electricity is passed through them ; but electricity passed 

 through air produces this effect. 



Reasoning ou this phenomenon, and on the extreme mobility of the 

 particles of air, I concluded, as M. Arago had likewise done from other 

 considerations, that the voltaic current in air would be affected by the 

 magnet. I failed in my first trial, which I have referred to in a note to my 

 former paper, and in other trials made since by using too weak a magnet ; 

 but I have lately had complete success : aud the experiment exhibits a very 

 striking phenomenon. 



3. Metals are well known to be capable of transmitting large 

 quantities of electricity; and one obvious limit to this quantity is 

 their fusion by the intensity of the heat thus excited, which inten- 

 sity is, of course, in part dependant upon the medium which 

 surrounds them ; thus, a platinum wire becomes much less 

 heated by the transmission of a certain quantity of electricity 

 when suspended in air, than when in the exhausted receiver of 

 an air-pump. Reasoning on this fact, it occurred to Sir 

 Humphry, 



That by placing wires in a medium much denser than air, such as ether, 

 alcohol, oils, or water, I might enable them to transmit a much liigher 

 charge of electricity than they could convey without being destroyed in 

 air ; and thus not only gain some new results as to the magnetic states of 

 such wires, but likewise, perhaps, determine the actual limits to the powers 

 of different bodies to conduct electricity, aud the relations of these powers. 



A wire of platinum of j^g, of three inches in length, was fused in air, by 

 being made to transmit the electricity of two batteries of ten zinc plates 

 of four inches with double copper, strongly charged: a similar wire was 

 placed in sulphuric ether, and the charge transmitted through it. It became 

 surrounded by globules of gas ; but no other change took place ; and in 

 this situation it bore tlie discharge from twelve batteries of the same kind, 

 exhibiting the same phenomena. When only about an inch of it was 

 heated by this high power in ether, it made the ether boil, and became 

 white hot under the globules of vapour, and then rapidly decomposed the 

 ether, but it did not fuse. When oil or water was substituted lor the ether, 

 the length of the wire remaining the same, it was partially covered with 

 small globules of gas, but did not become red hot. 



To ascertain whether short lengths of fine wire, prevented 

 from fusion by immersion in a cooling medium, transmitted the 

 whole electricity of large batteries, a second independent cir- 

 cuit was so made from the ends of the battery by silver wires in 

 water, that the decomposition of the water indicated the resi- 

 duary electricity. It was thus found that an inch in length of 

 platinum wire of one 220th of an inch diameter, kept cool by 

 water, left a great residual charge of electricity in a combina- 



