TRANSACTIONS OF THE SECTIONS. 25 



On an Induction-coil, spedcdly arranged for use in Spectrum Analysis, 

 By John Beowning, F.B.A.S. 



When an induction-coil is used for the purpose of burning metals, it is necessary 

 to interpose one or more I^eyden jars in the current. Such an arrangement though 

 efficient is inconvenient. The glass jars are liable to fracture, are bulky, and re- 

 quire to be dry to perform -well ; and the wires connecting them with the coil are 

 m the way and liable to derangement. 



To obviate these difficulties I constructed a form of apparatus which consists es- 

 sentially of a flat mahogany box filled with plates of ebonite, which are coated on 

 each side with tinfoil to within an inch of the edges. The contrivance generally 

 used for holding the metal or containing the gas under examination is packed inside 

 the lid of the box. When in use, this fits into a hollow screw on the top of the box. 

 To set this apparatus in motion, it is only necessary to carry a fine ■vnre. from each 

 of the terminals of the induction-coil and insert it in the connexions provided at 

 each end of the box, as these are connected with the tinfoil with which the ebonite 

 plates are coated. 



Mr. Spottiswoode suggested that there should be a contrivance added, by which 

 a greater or less number of the coated plates may be brought into action at -will. 

 This arrangement is very useful, as it enables the temperature of the spark to be 

 regulated. 



The simplest and best method of employing the coated ebonite plates, however, 

 is to place them in the base of the induction-coil, vmderneath the ordinary con- 

 denser, and connect them with the terminals. When thus arranged, the dense thick 

 spark may be obtained from any substance placed between the terminals of the coil, 

 or in any apparatus which may be attached to them, and a great economy of time 

 is eflected. 



On the Maximum amount of Magnetic Power wMcli can he develojyed by a 

 given Galvanic Battery. By H. Hightoit. 



The author's object was to show that by means of any galvanic battery whatever 

 electro-magnets might be made capable of sustaining any amount of weight without 

 limit. It was shown, both by mathematical formulae and experiment, that this was 

 the case, as also that a constant weight could be sustained, while the expenditure 

 of zinc in the battery could be at the same time continually diminished without 

 limit. In the discussion which followed, it was pointed out that this was a mere 

 power of sustaining weights, and not an energy such as could be applied to working 

 an electro-magnetic engine ; for that if the magnets were used to work an engine, 

 the currents produced by the reaction would cause an increased consumption of zinc. 



Letter from Dr. Joule, F.E.S., on a New Dip-Circle. 



My ueab Sin, — I communicated to the Exeter Meeting of the Association'a short 

 account of a new dip-circle, the peculiarity of wliich consisted in the suspension of 

 the axis of the needle by filaments of silk, of which the extremities were hung from 

 the arms of a delicate balance beam. I had hoped to exhibit the instrument to the 

 Section, but have found myself unable to attend the Meeting. It may, however, 

 be interesting to magnetic observers if I state that my experience during the year 

 has fuUy borne out the superiority of the new inclinometer over the ordinary fonn 

 of instrument. The facility of observation with it is such that six complete obser- 

 vations of the dip can be obtained in one hour, the average error of a single observa- 

 tion being a small fraction of a minute of arc. I am now giving still further deli- 

 cacy to the instrument by substituting spider- threads for silk, and am obviating the 

 danger of rust by using platina for the axis of the needle instead of steel, the softness 

 of the former metal being unobjectionable since the agate-plates are dispensed with. 



Believe me, yours most truly. 



Professor J. C. Maxwell. J^^^'S P. Joule. 



