Mullzform Apparatus.-In

order to double the

power to be obtained from

a single apparatus at

stations where lights of

exceptionally high intensity

are desired, the ex-, ,-,)

pedient of placing one, fit 'I

complete lens apparatus "

above another has sometimes

been adopted, as at

the Bishop Rock (Hg. I3),

and at the Fastnet light- 1

house in Ireland (Plate I.,

f1g.54). Triformandquad- gifgg;

riform apparatus have also, § . 1. . . been erected in Ireland; Eg; ~—- — Il:rl- '::f:jf '.ZI Q.j ¥=© particulars of the Tory:§ :§ :§ ¢ ~— —~- Q Island triform apparatus I Il , will be found in table VII. l ' r-The adoption of the multi- § ;Z;!;2;2g form system involves the ""' " " ' "“ use cghlanlferns of increase

eig t. q, ' /, V "' », , J ' J Twin A.p., ., .§ ., / .W W “ Q R A Another method of doub- '

ling the power of a light is V, % H I I § ~ by mounting two complete /I /E 1 lil 1|;- . 'and distinct optics side by / I I = " side on the same revolving / I I N D'a8"'3-'“ °fF1s=h°9 table, as I shown in fig. 43 , “ l ' Hash 0.3 of the Ile Vierge appar- ' ~ ' i., ' it L: " 5c, , p, , 7,2 atus. Several such lights j, “' 3, ,. ' I E, ,,8 have been installed by fl!" '- -“' ~. I ' * ghe French Lighthouse Iervxce.

Port Lights.-Small self- contained lanterns and ig ts are in common use for marking the entrances - to harbours and in other

similar }positions where neither igh power nor long range is requisite. Many such lights are un- attended in the sense that they do not require the attention of a keeper for days and even weeks These are de- scribed in more detail in section 6 of this article. Q typical port light con- sists of a copper or brass lantern containing a lens of the fourth order (250 D in ':ai ' Q mm. focald distance) ol; g I .; ' / Q, 'smaller, an a sing e wic, ,' § 'j '. il /// 1,5or 2-wick Argand capillary t , I . . , , wi .3 burner. Duplex burners " I, L ' 1/ are also used. The appar- si" I, 's . / / ' "atus may exhibit a fixed || l é

light or, more usually, an ll ' #N occulting characteristic is 1; - ' 5/ .Q ts produced by the revolu- " [I | ' | 'T ', tion of scfeelns acliuated bg | I i  :: - ' ta spring c oc wor aroun 'H, L'!£ I . the burner. The lantern may be placed at the top H ...S-A'-r ", of a column, or suspended Meycwy r/out I, from the head of a mast. i '; § .3 Coal gas and electricity are also used as illumiraants i i i i i ~ “I for port lights when oca " .U — E Q Q, ", 'L supplies are available. The " - mmm |'“"!l l 2 [HHu"“lmll[l , , optical apparatus used in ¢ . -, f, -;j ~ I Connexion with electric 5'€£.Q IQ. light is described below. . "““ "Orders" of Apparatus. ' ' C36/n f, ,1/fum. cz -Augustin Fresnel divided L . . rl the dioptric lenses, de- 'W " "" °'”” " signed by him, into“orders” .. .. . ~'T~<'* "§ I f 'W , ri>r sizes depending on their ll 2 5 I oca distance. This divi- f/ ii in ii 7 ' %Q7”§ I sion isgéill usfid, although % ll! 'W ! 'Ill two a itiona “ orders, ” /"T" ' W "' "KZ" "" // / known as “small third 7 = Jl= /// order"and “hyper-radial" /, / EE V M f°=0ef'fively are in ordinary

use The following

FIG. 41.-'MZHOYQ Point Apparatus and Lantern.