424
Class 10.—PHILOSOPHICAL, MUSICAL, HOROLOGICAL , " [Unitep
North, North Central, and South Central Galleries.
equal to the difference of the expansion of the glass rod jand the zinc tubes, between the clamps VV ; and thus the jtorsion force is diminished ; the position of the clamps is :so adjusted, that the diminution of the torsion force shall :be equivalent to the loss of power in the maguet; and :vice versa, when the temperature falls. The magnet,its appendages, and the suspension skein are enclosed 1similarly to the declination magnet; the glass box, &c., is !omitted to avoid confusion. The registration of its move-ments is likewise similarly effected on the opposite side ofthe cylinders.
4. A blackened zinc case, which is placed over thecylinders, when in actual operation, to prevent any lightfrom falling on the paper, except the two pencils whichdescribe the magnetic curves, and another which passesthrough a prism on' the top of the case, and draws thebase line. N.B.—This prism is placed on the top of theglass case, to show its proper position.
5. A case of the same material, which covers the wholeof the apparatus, to protect the sensitive paper from anystray light, as well as to defend the whole from dust, &c.
6. A balanced magnetometer, supported by agate knife-edges, resting on agate planes. The variations of thisinstrument are similarly recorded on—
7. A registering apparatus, similar to the precedingNo. 3, except that the axis of the revolving cylinder isvertical. The top of the inner cylinder rests on a turn-table, which is carried round by the hour-hand of atimepiece. In this and in the preceding apparatus, thelines of light reflected from the specula are each reducedto a point, by passing through two cylindrical planeconvex lenses placed near the sides of the cylinders.
8. A self-registering barometer. The short arm of alever carries a float which rests on the surface of themercury in the lower end of a syphon barometer tube.The long arm carries a light screen with a small aperturein it, which is interposed between the revolving cylinderof No. 5, and a light. The small pencil of light passingthrough the screen marks the photographic paper, andthus records the changes in the mercurial column. Thesame light which registers the barometer serves also todescribe the base line for the magnetic curve, by a pencilconducted from the back of the chimney through a tubewith a right-angled prism at each end of it. This instru-ment is shown in fig. 2.
AA, a self-registering barometer, enclosed in a case,resting on a stand.
BB, the upper and lower ends of a syphon barometer,which are of the same diameter, and of large size.
C, a float resting on the surface of the mercury, whichhangs in a notch on the short arm of a lever.
D, the pivot on which the lever turns.
E, the long arm of the lever, which carries at its ex-tremity an opaque screen F, with a small aperture,through which a small pencil of light passes.
G, a plate on which the tube rests, which is raised orlowered by a screw.
H, a stand supporting a gas-burner.
I, the register line, described by this pencil of light.The screen F will evidently rise and fall with the columnof mercury, and the indications will be amplified in pro-portion to the length of leverage.
K, a tube with a plano-convex prismatic lens at eachend of it, placed at the back of the burner; through this,a pencil of light is conducted in the direction indicatedby the dotted line, and describes the base line L. Bythis arrangement, two pencils are derived from the samesource of light, which fall perpendicularly on two remotepoints of the paper.
M, the balanced magnetometer.
N, a concave speculum connected with the magnet bya bar, to which are attached agate knife edges; these reston agate planes attached to the supporting frame.
O, a plane mirror for making observations with a tele-scope in the usual manner.
P, a gas-burner, from which a pencil of light is reflectedfrom the speculum N, and passing through a combinationof two piano-cylindrical lenses in the frame Q, describesthe register line R.
Brooke’s Self-registering Barometer.
S, a frame supporting a turn-table.
T, the cylinder resting on the turn-table.
V, the gas-pipe supplying the burners.
9 and 10. Zinc cases analogous to 4 and 5. . 6
11. A wet and dry-bulb thermometer, and app ar ^. g ,for registering the temperature they indicate. The re ® - ctering apparatus consists of a pair of vertical conceii ^cylinders, similar to No. 7, supported on a table.bulbs of the thermometers are underneath the t a lthrough which the stems pass vertically, and are P® 0between the opposite sides of the cylinders and uSlights. A narrow vertical line of light brought toat ^by a cylindrical lens, falls on the stem of the thei ^meter, and passing through the empty portion of the ,affects the paper. The boundary between the darKLand undarkened portion indicates the position ot emercury in the stem of the thermometer. Five wires ^placed across the slit in the frame, through whi ca . slight falls on the stem. They intercept narrow p 0 *’of the light, and thus the scale of the thermoinetecontinuously impressed on the register, as well astemperature. This instrument is shown in fig. 3.
I , 2, camphine lamps. ,
3, 4, cylindrical lenses, by which a bright fo ca
of light is obtained.
5, the psychrometer, or wet-bulb thermometer.
6, the dry-bulb thermometer. . , p ho-
7, two concentric cylinders, between which tn V
tographic paper is placed. . is
8, the register, as it appears after the impre
developed. , • u Cxe
9, one of the rollers of a turn-table, on wn
cylinders rest.
10, the frame which contains the timepiece. ^
II, a bent pin, or carrier, attached to the axi ^ t j ie
cylinders ; this is carried round by a toi
end of the hour-hand of the timepiece.