TRANSACTIONS OF SECTION A. 617 



ebonite tube ^ inch in thickness. A pole-piece is screwed on to each end of the 

 core. 



The secondary is wound in 52 sections, having an average of about 1,200 turns 

 of wire to each section, taking in all 14^ miles of double silk covered copper wire, 

 Nos. 35 and 36 B.W.G. The maximum outer diameter of secondary is 5^ inches in 

 the middle, and the minimum at ends is Sy inches, the inner diameter 2| at the 

 middle and 2| at each end; the length of secondary body is 11 inches, the 

 terminals lOjj inches asunder. 



There are three condensers of 40, 30, and 20 sheets of tinfoil respectively, 

 the sheets being 10 x 7|. 



The vibrating spring of contact-breaker is cut in two near the foot, and a 

 tongue of hardened and tempered steel let in and securely riveted. 



This principle is found to be of great use in photography, the spectra of metals, 

 and gases, as the vibrations are accelerated thereby. 



The main feature, however, resides in the new method of insulation between 

 the sections, the thickness of insulation being made to vary as the diii'erences of 

 potential between the parts of any two adjoining sections. 



The coil is capable of giving sparks between nine and ten inches in length, with 

 one quart bickromate cell. With this instrument and the photographic apparatus 

 described on a former occasion, the author proposes to photograph and map the 

 specti-a of chemical elements, the solar lines, and those of the spectrum of iron to. 

 be used as reference lines. The lo.l.^s for a considerable portion may be obtained 

 from Professor llowland's normal map by simple inspection ; but throughout the 

 w.l. according to Angstrom will be also used. The sheets will illustrate the plan 

 proposed. 



WEDNESDAY, SEPTEMBER 7. 



The following Reports and Papers were read : — 



]. Third Beport of the Committee on Standards of Light. — See Reports, 



p. 47. 



2. On a Standard Lamp. Sjj A. Vernon Hakcourt, M.A., F.B.S. 



At one of the meetings of this Section last year a lamp devised by the author 

 for producing a constant amount of light was shown and described by Mr. W. S. 

 Rawson. The lamp now exhibited served the same purpose, but was simpler in 

 principle, more easily adjusted, and less affected by draughts. It consisted of a 

 glass reservoir with tubulure and stopper, of the form and size of a large spirit 

 lamp, mounted on a metal stand provided with levelling screws. The wick could 

 be turned up and down in the usual manner within a long tube attached to the 

 body of the lamp. Round this tube is a wider tube 100 x 25 mm. ; and the two 

 being joined together above and below by flat plates constitute the burner of the 

 lamp. When the burner becomes warm by conduction of heat from the flame the 

 pentane which rises in the wick volatilises, and the vapour burns at a consider- 

 able distance above the point to which the wick is turned down. Thus the size 

 or texture or quality of the wick does not affect the flame. 



Around the burner and the lower part of the flame was another cylinder open 

 at both ends and contracted above the burner to a tube 20 mm. in diameter and in 

 length. A similar tube formed the lower part of an upper chimney which was 

 enlarged above to a diameter of 25 mm. The upper part of the flame was 

 concealed by this chimney excepting where a narrow slot 10 x 3 mm. on each side 

 showed the tip of the flame, and enabled its height to be regulated. Through the 

 interval between the two chimneys the flame shines, and the light which it gives is 

 the same whenever the tip of the flame is visible opposite the slot, whether towards- 

 the lower or the upper end. 



