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52 QOXIOMETEHS. p, q may be nearly perpendicular to ir K , and, therefore iik repeated. ^turb the former, the process must be try^i^en^um^ered with^ 33 usua % constructed in this coun turned in one direction oX^ 8 J° P ’ f ° WS the circle to be rately, at o° or 180° TP i i 8C "' es lk ’ not ve, 7 accu - the screws which fasten it" removed by taking out ton i?Sch ■». *- >- to from one face to the next ° 8 mCr0a8e “ paSS ' ng be ntwly eqXrand X X" , signals from the cr .>' stal should distant tihe better The ^ than . 8 “ , 0r ?* ht feet.* The more are made in the i , • u PP er S1 gnal, when the observations horizontal SitIn aXe T ’f * narr0W black bar > or a window, parallel to tl f “ P f 1 in - the U P per P art of a signal a whit-p r ax ’ s °f the circle; and the lower axis of the circle T ° n a k gr0und a,s0 parallel to the by a lens of short f n "i * ome J asca ai1 “nage of the sun, formed through which the r \ , en T, or a sniab round hole in a screen advantage for the unif< * " t* 7 ," 8C ° U ’ ” a7 b ° US ° d " ith r °w slits in screens thr X I obsc , rv l n ff at nfeht two nar- candle ami !, ens > trough one of which is seen the flame of a candle'placed'behmd f ° ther a ° f PapCr illuminated >7 a the sun fromT nknf^• 18 obtalaed . b 7 reflecting the light of opening i n a elite nf m ! r, ! or ’ or heliostat, through,a triangular diminished or^nlt Wh / ch ’ by mCan8 of a 8,i,icr ’ ™Y b * are more or less perfect ^PhT 7' ? T , thc f,l(3C8 of tll ° crystal sbt in a plate of metnl u • amt sl b mal 1,1 7 be a horizontal placed behind it viewmN™'' 1 ,? by a sbeet of wllito P a P Rr The signals A.Bmav the l reflexion ln a mirror of black glass, the observer, and need w i° noar ^ 0,1 11 level with the eye of each other. I n observi,, *1° moro tban s ' x inches distant from a face of the crystal is m j , lm! 7 e of ' a, seen by reflexion in seen by reflexion in ’ the mi ° coincide with the image of n about 40° with a hori/ontnT 1° P ’ ( i should make au angle of to the foot of the goniomete an °' Wbeu th c mirror is attached of the goniometer will not affect un8toa d | >'ess in the support It is not essential that the • a P carno y °f the observations. horizontal. A goniometer witl*' 8 ° goniometer should be t, woineter with a vertical axis, though perhaps