182 REPORT—1850. 
The figures 1 and 2 of Plate I. are drawn to one-eighth of the real size ; 
figures 3, 4, 5 and 6, to one-fourth of the size. The figures of Plate II. to 
one-quarter of the real size. 
V, figs. Land 2, Plate IL, is the magnet box (in section), of mahogany, not 
coated, as before, with gold paper, provided with a squared tube, ‘I, of cast 
brass, which opens into A. 
A is the camera box (of mahogany ). 
a is the usual solid brass casting, forming (in part) one of the ends of 
B is a fifteen-inch magnet belonging to a vertica]-force balance magneto- 
meter of Dr. Lloyd’s construction. 
62, a piece screwed upon the upper edge of B. 
b3, a pair of very light, sliding brass tubes attached to 6%, and capable of 
vertical adjustment (for length). 
ὖ5, a weight adjustable on a screw attached to the lower edge of B, for 
poising 63, χα. properly. 
b', the moveable shield, composed of very light sheet-brass, flat, and having 
its upper edgé curved to a radius of 12 inches, and attached to 63. It hasa 
very narrow slit at the centre of its upper edge. 
O is a diaphragm plate, whose aperture is about an inch long (horizontally), 
and a quarter of an inch wide ; it is supported by two angular plates (as 0°) 
resting upon X, and attached (with means of adjustment) to σ᾽ by screws 
passtng through slits. 
οἷ, the fixed shield attached to O by means of a little bolt, washers and 
nut, 0%. It is capable of adjustments for horizontality, height, &e. At about 
three-eighths of an inch from its centre is a slit, somewhat larger than the 
slit in B. The lower edge of this shield stands at about a twentieth of an 
inch lower than the upper edge of δ', and at about the same quantity from 
its interior plane. 
C is the shutter apparatus. 
δ᾽ is a plate screwed upon A, and having an aperture about equal to and 
corresponding with an aperture and little plate of glass in A. It is provided 
with grooved pieces, between which slides freely c®. 
65 is a plate having an aperture (03) equal to that of c' and A, but cor- 
responding with the latter only when it has slid into its lowest position. 
ct is a small line attached at one end to οἷ, passed over a pulley, 65, under 
another pulley, ¢°, and fixed to a lever, 67 (fig. 7, Plate I.), within the clock 
case K, which lever is attached to the apparatus used for stopping and start- 
ing the clock (vide k®, Plate II. of the Report of the British Association for 
1849). 
The object of this arrangement (C, &c.) is to admit light into A at the 
moment of starting the clock, and to exclude light therefrom at the moment 
of stopping it. 
Ὁ (Plate I. fig. 1) is a modification of Count Rumford’s polyflame lamp, 
having three flat wicks and rack-work to raise them. 
d', its high, squared copper chimney, with a narrow glass plate opposite to 
the best part of the flame. 
E (Plate II. fig. 1) is the mouth-piece, in section, consisting of two angular 
pieces and of two little plates attached to them, forming the lips and aper- 
ture e!, which aperture can be diminished or increased at pleasure, with great 
and requisite aceuracy ; for, 
is a plate screwed upon a’. 
εὃ & (fig. 3) are two screws, which, freely sliding through e* and screwing 
into the upper portion of E, are employed to elevate that portion. 
et is another screw, screwing through 65 and pressing occasignally upon 
