155 



of a wire, heated to dull redness in the circuit, is cooled by ice, the 

 remaining portion becomes white hot, whilst the application of the 

 flame of a spirit-lamp renders the other part colder. 



In discussing the relations of heat, magnetism, and chemical ac- 

 tion, to electricity, Sir Humphry particularly adverts to the relative 

 elevations of temperature which the different metals undergo during 

 the transmission of electricity : thus, when a chain, composed of al- 

 ternate lengths of silver and platinum is made the connecting me- 

 dium between the poles of a powerful battery, the silver wire being 

 four or five times the diameter of the platinum, the former metal is 

 not sensibly heated, whilst the latter becomes intensely ignited. 

 Now if heat be regarded as material, we cannot suppose that it is 

 expelled from the platinum because it may be thus generated in- 

 definitely ; again, if dependent upon, or identical with, electricity, 

 its quantity should be similar throughout the metallic chain. In re- 

 gard to the magnetism of this chain, the case is different, for every 

 part of it exhibits equal magnetic powers ; so that the power appears 

 directly as the quantity of electricity. 



Sir Humphry Davy concludes this communication with some ge- 

 neral remarks respecting the different phenomena produced by the 

 agency of electricity ; whether they depend upon one or more spe- 

 cies of ethereal matter, or whether they are merely exhibitions of the 

 attractive powers and subtile motions of the corpuscles of common 

 matter, are questions which remain for the determination of future 

 researches and experiments. 



The Bakerian Lecture. An Account of Experiments to determine the 

 Amount of the Dip of the Magnetic Needle in London, in August 

 1821; with Remarks on the Instruments which are usually employed 

 in such Determinations. By Captain Edward Sabine, of the Royal 

 Regiment of Artillery, F.R.S. Read November 22, 1821. [Phil. 

 Trans. 182*2, p. 1.] 



After describing the imperfections of the instruments in general 

 use for ascertaining the dip of the magnetic needle, and adverting to 

 the consequent inaccuracy and insufficiency of the observations made 

 with them, Captain Sabine gives an account of the form of dipping- 

 needle which he preferred for his experiments, and which was con- 

 structed for him by Mr. Dollond, upon principles laid down by Pro- 

 fessor Meyer, of Gottingen. He then enters into minute details of 

 the mode of pursuing and verifying his observations, the results of 

 which, gained by three different methods, are as follows : viz. by 10 

 experiments with Meyer's needle, 70 2' - 9 ; by the times of oscil- 

 lation in the magnetic meridian, and in the plane perpendicular to it 

 (mean by three needles), 70 04' ; by the times of vertical and hori- 

 zontal oscillation, 7 02'- 6. So that 70 03' may be considered as 

 the mean dip of the needle towards the north, in August and Sep- 

 tember 1821, within four hours of noon, being the limit within which 

 all the experiments were made. 



